Isomers.( This article is under construction. )

Isomer

In chemistry, isomers (pronounced /ˈaɪsəmə(ɹ)z/; from Greek ἰσομερής, isomerès; isos = "equal", méros = "part") are compounds with the same molecular formula but different structural formulas.
Isomers do not necessarily share similar properties, unless they also have the same functional groups.
There are many different classes of isomers, like
    stereoisomers,
    enantiomers,
    geometrical isomers, etc.
There are two main forms of isomerism:
    structural isomerism and
    stereoisomerism (spatial isomerism).


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Structural isomer
Structural isomerism, or constitutional isomerism (per IUPAC), is a form of isomerism in which molecules with the same molecular formula have bonded together in different orders, as opposed to stereoisomerism.
There are multiple synonyms for constitutional isomers.

Three categories of constitutional isomers are skeletal, positional, and functional isomers. Positional isomers are also called regioisomers. Tautomers are subcategory of functional isomers.
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Chain(Skeletal) isomerism
In chain isomerism, or skeletal isomerism, components of the (usually carbon) skeleton are distinctly re-ordered to create different structures.
Pentane exists as three isomers: n-pentane (often called simply "pentane"), isopentane (2-methylbutane) and neopentane (dimethylpropane).
===Images===============3 k =======================================

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Position isomerism
In position isomerism a functional group or other substituent changes position on a parent structure.
As in below, the hydroxyl group can occupy three different positions on an n-pentane chain forming three different compounds.
=======Images=======3 k ===========================
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Functional group isomerism
Functional isomers are structural isomers that have the same molecular formula (that is, the same number of atoms of the same elements), but the atoms are connected in different ways so that the groupings are dissimilar.
These groups of atoms are called functional groups, functionalities, or moieties.
Another way to say this is that two compounds with the same molecular formula, but different functional groups, are functional isomers.
For example, cyclohexane and 1-hexene both have the formula C6H12. These two are considered functional group isomers because cyclohexane is a cycloalkane and hex-1-ene is an alkene.
=======Images=======2 k =============
For two molecules to be functional isomers, they must contain key groups of atoms arranged in particular ways.
Some of the best examples come from organic chemistry. C2H6O is a molecular formula. Depending on how the atoms are arranged, it can represent two different compounds
    dimethyl ether CH3-O-CH3 or
    ethanol CH3CH2-O-H
Dimethyl ether and ethanol are functional isomers.
The first is an ether. The carbon chain-oxygen-carbon chain functionality is called an ether.
The second is an alcohol. The carbon chain-oxygen-hydrogen functionality is called an alcohol.

If the functionalities stay the same, but their locations change, the structural isomers are not functional isomers. 1-Propanol and 2-propanol are structural isomers, but they are not functional isomers. Both of them are alcohols.
The functional group (carbon chain-O-H) is present in both of these compounds, but they are not the same.

note:While some chemists use the terms structural isomer and functional isomer interchangeably, not all structural isomers are functional isomers.

Functional isomers are most often identified in chemistry using infrared spectroscopy.
Infrared radiation corresponds to the energies associated primarily with molecular vibration.
The alcohol functionality has a very distinct vibration called OH-stretch that is due to hydrogen bonding.
All alcohols in liquid and solid form absorb infrared radiation at certain wavelengths.

Compounds with the same functional groups will all absorb certain wavelengths of infrared light because of the vibrations associated with those groups.
In fact, the infrared spectrum is divided into two regions.
The first part is called the functional group region.
Dimethyl ether and ethanol would have dissimilar infrared spectra in the functional group region.

The second part of the infrared spectrum is called the fingerprint region; it is associated with types of motion allowed by the symmetry of the molecule and influenced by the bond energies.
The fingerprint region is more specific to an individual compound. Even though 1-propanol and 2-propanol have similar infrared spectra in the functional group region, they differ in the fingerprint region.

In simple terms, functional isomers are structural isomers that have different functional groups like alcohol and ether.

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Electrone

                          Electrone

 
Definition.
Properties.
Creation.
Annihilation.



Definition.( What is electrone )
The electron (symbol: e⁻) is a subatomic particle with a negative elementary electric charge.

Properties.

• An electron has no known components or substructure.It is generally thought to be an elementary particle.

• An electron has a mass that is approximately 1/1836 that of the proton.

• The intrinsic angular momentum (spin) of the electron is a half-integer value in units of ħ, which means that it is a fermion. ( Since an electron is a fermion, no two electrons can occupy the same quantum state, in accordance with the Pauli exclusion principle. )

• The antiparticle of the electron is called the positron; it is identical to the electron except that it carries electrical and other charges of the opposite sign.

• When an electron collides with a positron, both particles may be totally annihilated, producing gamma ray photons.

• Like all matter, they have quantum mechanical properties of both particles and waves, so they can collide with other particles and can be diffracted like light.

• However, this duality is best demonstrated in experiments with electrons, due to their tiny mass.

• An electron in motion relative to an observer generates a magnetic field, and will be deflected by external magnetic fields.

• When an electron is accelerated, it can absorb or radiate energy in the form of photons.

• Electrons contribute less than 0.06% to an atom's total mass.

• The exchange or sharing of the electrons between two or more atoms is the main cause of chemical bonding.

Creation.
Electrons may be created through beta decay of radioactive isotopes and in high-energy collisions, for instance when cosmic rays enter the atmosphere.

Annihilation.
Electrons may be destroyed through annihilation with positrons, and may be absorbed during nucleosynthesis in stars.

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ChemRun The trust you feel
Hope for more , coming up , just wait

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Silicon

Silicon

 















Overview.
Silicon, a tetravalent metalloid, is a chemical element with the symbol Si and atomic number 14.
It is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium.
Controversy about silicon's character dates to its discovery: silicon was first prepared and characterized in pure form in 1823. In 1808, it was given the name silicium (from Latin: silicis, flints), with an -ium word-ending to suggest a metal, a name which the element retains in several non-English languages.
However, its final English name, first suggested in 1817, reflects the more physically similar elements carbon and boron.

Silicon is the eighth most common element in the universe by mass, but very rarely occurs as the pure free element in nature.
It is most widely distributed in
    dusts,
    sands,
    planetoids, and
    planets as various forms of silicon dioxide (silica) or silicates.
Over 90% of the Earth's crust is composed of silicate minerals, making silicon the second most abundant element in the Earth's crust (about 28% by mass) after oxygen.

Most silicon is used commercially without being separated, and indeed often with little processing of compounds from nature.
These include direct industrial building-use of clays, silica sand and stone.
Silica is used in ceramic brick.
Silicate goes into Portland cement for mortar and stucco, and when combined with silica sand and gravel, to make concrete.
Silicates are also in whiteware ceramics such as porcelain, and in traditional quartz-based soda-lime glass.
More modern silicon compounds such as silicon carbide form abrasives and high-strength ceramics.
Silicon is the basis of the ubiquitous synthetic silicon-based polymers called silicones.
Elemental silicon also has a large impact on the modern world economy.
Although most free silicon is used in the steel refining, aluminum-casting, and fine chemical industries (often to make fumed silica), the relatively small portion of very highly purified silicon that is used in semiconductor electronics (< 10%) is perhaps even more critical. Because of wide use of silicon in integrated circuits, the basis of most computers, a great deal of modern technology depends on it.


Physical characteristics
Silicon is a solid at room temperature, with relatively high melting and boiling points of approximately 1,400 and 2,800 degrees Celsius respectively.
Interestingly, silicon has a greater density in a liquid state than a solid state. It does not contract when it freezes like most substances, but expands, similar to how ice is less dense than water and has less mass per unit of volume than liquid water.
With a relatively high thermal conductivity of 149 W·m−1·K−1, silicon conducts heat well and as a result is not often used to insulate hot objects.

In its crystalline form, pure silicon has a gray color and a metallic luster. Like germanium, silicon is rather strong, very brittle, and prone to chipping.
Silicon, like carbon and germanium, crystallizes in a diamond cubic crystal structure, with a lattice spacing of 0.5430710 nm (5.430710 Å).

The outer electron orbital of silicon, like that of carbon, has four valence electrons.
The 1s, 2s, 2p and 3s subshells are completely filled while the 3p subshell contains two electrons out of a possible six.
Electrone configuration 
    1S2 2S22P6 3S23P2

Silicon is a semiconductor. It has a negative temperature coefficient of resistance, since the number of free charge carriers increases with temperature.
The electrical resistance of single crystal silicon significantly changes under the application of mechanical stress due to the piezoresistive effect.


Chemical characteristics.
Silicon is a metalloid, readily either donating or sharing its four outer electrons, allowing for many forms of chemical bonding.
Like carbon, it typically forms four bonds.
Unlike carbon, it can accept additional electrons and form five or six bonds in a sometimes more labile silicate form.
Tetra-valent silicon is relatively inert, but still reacts with halogens and dilute alkalis, but most acids (except for some hyper-reactive combinations of nitric acid and hydrofluoric acid) have no known effect on it.
However, having four bonding electrons gives it, like carbon, many opportunities to combine with other elements or compounds under the right circumstances.


Isotopes
Naturally occurring silicon is composed of three stable isotopes, silicon-28, silicon-29, and silicon-30, with silicon-28 being the most abundant (92% natural abundance).
Out of these, only silicon-29 is of use in NMR and EPR spectroscopy. Twenty radioisotopes have been characterized, with the most stable being silicon-32 with a half-life of 170 years, and silicon-31 with a half-life of 157.3 minutes.
All of the remaining radioactive isotopes have half-lives that are less than seven seconds, and the majority of these have half-lives that are less than one tenth of a second.

Silicon does not have any known nuclear isomers.

The isotopes of silicon range in mass number from 22 to 44.
The most common decay mode of six isotopes with mass numbers lower than the most abundant stable isotope, silicon-28, is β+, primarily forming aluminium isotopes (13 protons) as decay products.
The most common decay mode(s) for 16 isotopes with mass numbers higher than silicon-28 is β−, primarily forming phosphorus isotopes (15 protons) as decay products.




Compounds
    Silicon forms binary compounds called silicides with many metallic elements whose properties range from reactive compounds, e.g. magnesium silicide, Mg2Si through high melting refractory compounds such as molybdenum disilicide, MoSi2.
    Silicon carbide, SiC (carborundum) is a hard, high melting solid and a well known abrasive. It may also be sintered into a type of high-strength ceramic used in armor.
    Silane, SiH4, is a pyrophoric gas with a similar tetrahedral structure to methane, CH4. When pure, it does not react with pure water or dilute acids; however, even small amounts of alkali impurities from the laboratory glass can result in a rapid hydrolysis.There is a range of catenated silicon hydrides that form a homologous series of compounds, Si(n)H(2n+2) where n = 2–8 (analogous to the alkanes). These are all readily hydrolyzed and are thermally unstable, particularly the heavier members.
    Disilenes contain a silicon-silicon double bond (analogous to the alkenes) and are generally highly reactive requiring large substituent groups to stabilize them.A disilyne with a silicon-silicon triple bond was first isolated in 2004; although as the compound is non-linear, the bonding is dissimilar to that in alkynes.
    Tetrahalides, SiX4, are formed with all the halogens.Silicon tetrachloride, for example, reacts with water, unlike its carbon analogue, carbon tetrachloride.Silicon dihalides are formed by the high temperature reaction of tetrahalides and silicon; with a structure analogous to a carbene they are reactive compounds. Silicon difluoride condenses to form a polymeric compound, (SiF2)n.
=========Image==================(SiF2)n==================================
    Silicon dioxide is a high melting solid with a number of crystal forms; the most familiar of which is the mineral quartz. In quartz each silicon atom is surrounded by four oxygen atoms that bridge to other silicon atoms to form a three dimensional lattice. Silica is soluble in water at high temperatures forming a range of compounds called monosilicic acid, Si(OH)4. (Also can be called as H2SiO3; really this is the way
Si(OH)4 conains 4H,4O  and 1Si, consider that if one H2O goes away form that...)
    Under the right conditions monosilicic acid readily polymerizes to form more complex silicic acids, ranging from the simplest condensate, disilicic acid (H6Si2O7) to linear, ribbon, layer and lattice structures which form the basis of the many silicate minerals and are called polysilicic acids {Six(OH)4–2x}n.
    With oxides of other elements the high temperature reaction of silicon dioxide can give a wide range of glasses with various properties.Examples include soda lime glass, borosilicate glass and lead crystal glass.
    Silicon sulfide, SiS2 is a polymeric solid (unlike its carbon analogue the liquid CS2).
    Silicon forms a nitride, Si3N4 which is a ceramic.Silatranes, a group of tricyclic compounds containing five-coordinate silicon, may have physiological properties.
    Many transition metal complexes containing a metal-silicon bond are now known, which include complexes containing SiHnX3−n ligands, SiX3 ligands, and Si(OR)3 ligands.
    Silicones are large group of polymeric compounds with an (Si-O-Si) backbone. An example is the silicone oil PDMS (polydimethylsiloxane). These polymers can be crosslinked to produce resins and elastomers.
    Many organosilicon compounds are known which contain a silicon-carbon single bond. Many of these are based on a central tetrahedral silicon atom, and some are optically active when central chirality exists. Long chain polymers containing a silicon backbone are known, such as polydimethysilylene (SiMe2)n.Polycarbosilane, [(SiMe2)2CH2]n with a backbone containing a repeating -Si-Si-C unit, is a precursor in the production of silicon carbide fibers.

 Production
Alloys
Ferrosilicon, an iron-silicon alloy that contains varying ratios of elemental silicon and iron, accounts for about 80% of the world's production of elemental silicon, with China, the leading supplier of elemental silicon, providing 4.6 million tonnes (or 2/3 of the world output) of silicon, most of which is in the form of ferrosilicon. It is followed by Russia (610,000 t), Norway (330,000 t), Brazil (240,000 t) and the United States (170,000 t).Ferrosilicon is primarily used by the steel industry.

Aluminum-silicon alloys are heavily used in the aluminum alloy casting industry, where silicon is the single most important additive to aluminum to improve its casting properties. Since cast aluminum is widely used in the automobile industry, this use of silicon is thus the single largest industrial use of "metallurgical grade" pure silicon (as this purified silicon is added to pure aluminum, whereas ferrosilicon is never purified before being added to steel).


 Metallurgical grade
Elemental silicon not alloyed with significant quantities of other elements, and usually > 95%, is often referred to loosely as silicon metal.
It makes up about 20% of the world total elemental silicon production, with less than 1 to 2% of total elemental silicon (5–10% of metallurgical grade silicon) ever purified to higher grades for use in electronics. Metallurgical grade silicon is commercially prepared by the reaction of high-purity silica with wood, charcoal, and coal in an electric arc furnace using carbon electrodes. At temperatures over 1,900 °C (3,450 °F), the carbon in the aforementioned materials and the silicon undergo the chemical reaction
    SiO2 + 2 C → Si + 2 CO

Liquid silicon collects in the bottom of the furnace, which is then drained and cooled. The silicon produced this manner is called metallurgical grade silicon and is at least 98% pure.
Using this method, silicon carbide (SiC) may also form from an excess of carbon in one or both of the following ways:
    SiO2 + C → SiO + CO     or
    SiO + 2 C → SiC + CO
 However, provided the concentration of SiO2 is kept high, the silicon carbide can be eliminated by the chemical reaction
    2 SiC + SiO2 → 3 Si + 2 CO.

As noted above, metallurgical grade silicon "metal" has its primary use in the aluminum casting industry to make aluminum-silicon alloy parts. The remainder (about 45%) is used by the chemical industry, where it is primarily employed to make fumed silica.

As of September 2008, metallurgical grade silicon costs about US$1.45 per pound ($3.20/kg), up from $0.77 per pound ($1.70/kg) in 2005.


Electronic grade
The use of silicon in semiconductor devices demands a much greater purity than afforded by metallurgical grade silicon. Very pure silicon (>99.9%) can be extracted directly from solid silica or other silicon compounds by molten salt electrolysis.
This method, known as early as 1854, has the potential to directly produce solar-grade silicon without any carbon dioxide emission at much lower energy consumption.

Solar grade silicon cannot be used for semiconductors, where purity must be extreme to properly control the process.
Bulk silicon wafers used at the beginning of the integrated circuit making process must first be refined to "nine nines" purity (99.9999999%), a process which requires repeated applications of refining technology.

The majority of silicon crystals grown for device production are produced by the Czochralski process, (CZ-Si) since it is the cheapest method available and it is capable of producing large size crystals.
However, single crystals grown by the Czochralski process contain impurities because the crucible containing the melt often dissolves. Historically, a number of methods have been used to produce ultra-high-purity silicon.

Early silicon purification techniques were based on the fact that if silicon is melted and re-solidified, the last parts of the mass to solidify contain most of the impurities. The earliest method of silicon purification, first described in 1919 and used on a limited basis to make radar components during World War II, involved crushing metallurgical grade silicon and then partially dissolving the silicon powder in an acid. When crushed, the silicon cracked so that the weaker impurity-rich regions were on the outside of the resulting grains of silicon. As a result, the impurity-rich silicon was the first to be dissolved when treated with acid, leaving behind a more pure product.

In zone melting, also called zone refining, the first silicon purification method to be widely used industrially, rods of metallurgical grade silicon are heated to melt at one end. Then, the heater is slowly moved down the length of the rod, keeping a small length of the rod molten as the silicon cools and re-solidifies behind it. Since most impurities tend to remain in the molten region rather than re-solidify, when the process is complete, most of the impurities in the rod will have been moved into the end that was the last to be melted. This end is then cut off and discarded, and the process repeated if a still higher purity is desired.

At one time, DuPont produced ultra-pure silicon by reacting silicon tetrachloride with high-purity zinc vapors at 950 °C, producing silicon by
    SiCl4 + 2 Zn → Si + 2 ZnCl2
However, this technique was plagued with practical problems (such as the zinc chloride byproduct solidifying and clogging lines) and was eventually abandoned in favor of the Siemens process. In the Siemens process, high-purity silicon rods are exposed to trichlorosilane at 1150 °C. The trichlorosilane gas decomposes and deposits additional silicon onto the rods, enlarging them because
    2 HSiCl3 → Si + 2 HCl + SiCl4
Silicon produced from this and similar processes is called polycrystalline silicon. Polycrystalline silicon typically has impurity levels of less than one part per billion.(1 ppb )

In 2006 REC announced construction of a plant based on fluidized bed (FB) technology using silane:     3 SiCl4 + Si + 2 H2 → 4 HSiCl3
    4 HSiCl3 → 3 SiCl4 + SiH4
    SiH4 → Si + 2 H2
The advantage of fluid bed technology is that processes can be run continuously, yielding higher yields than Siemens Process, which is a batch process.

Today, silicon is purified by converting it to a silicon compound that can be more easily purified by distillation than in its original state, and then converting that silicon compound back into pure silicon. Trichlorosilane is the silicon compound most commonly used as the intermediate, although silicon tetrachloride and silane are also used. When these gases are blown over silicon at high temperature, they decompose to high-purity silicon.
=========================Image==== Trichlorosilane=====================

In addition, there is the Schumacher process, which utilizes tribromosilane in place of trichlorosilane and fluid bed technology. It requires lower deposition temperatures, lower capital costs to build facilities and operate, no hazardous polymers nor explosive material, and produces no amorphous silicon dust waste, all of which are drawbacks of the Siemens process.However, there are yet to be any major factories built using this process.



Applications

Compounds
Most silicon is used industrially without being separated into the element, and indeed often with comparatively little processing from natural occurrence. Over 90% of the Earth's crust is composed of silicate minerals. Many of these have direct commercial uses, such as
    clays, silica sand and
    most kinds of building stone.
Thus, the vast majority of uses for silicon are as structural compounds, either as the silicate minerals or silica (crude silicon dioxide). For example, silica is an important part of ceramic brick. Silicates are used in making Portland cement which is used in building mortar and stucco, but more importantly combined with silica sand, and gravel (usually containing silicate minerals like granite), to make the concrete that is the basis of most of the very largest industrial building projects of the modern world.

Silicate minerals are also in whiteware ceramics, an important class of products usually containing various types of fired clay (natural aluminum silicate). An example is porcelain which is based on silicate mineral kaolinite. Ceramics include art objects, and domestic, industrial and building products. Traditional quartz-based soda-lime glass also functions in many of the same roles.
More modern silicon compounds also function as high-technology abrasives and new high-strength ceramics based upon (silicon carbide), and in superalloys.

Alternating silicon-oxygen chains with hydrogen attached to the remaining silicon bonds form the ubiquitous silicon-based polymeric materials known as silicones. These compounds containing silicon-oxygen and occasionally silicon-carbon bonds have the capability to act as bonding intermediates between glass and organic compounds, and to form polymers with useful properties such as impermeability to water, flexibility and resistance to chemical attack. Silicones are often used in waterproofing treatments, molding compounds, mold-release agents, mechanical seals, high temperature greases and waxes, and caulking compounds. Silicone is also sometimes used in breast implants, contact lenses, explosives and pyrotechnics.Silly Putty was originally made by adding boric acid to silicone oil.


Alloys
Elemental silicon is added to molten cast iron as ferrosilicon or silicocalcium alloys to improve performance in casting thin sections, and to prevent the formation of cementite where exposed to outside air. The presence of elemental silicon in molten iron acts as a sink for oxygen, so that the steel carbon content, which must be kept within narrow limits for each type of steel, can be more closely controlled. Ferrosilicon production and use is a monitor of the steel industry, and although this form of elemental silicon is impure, it accounts for 80% of the world's use of free silicon.

The properties of silicon itself can be used to modify alloys. Silicon's importance in aluminum casting is that a significantly high amount (12%) of silicon in aluminum forms a eutectic mixture which solidifies with very little thermal contraction. This greatly reduces tearing and cracks formed from stress as casting alloys cool to solidity. Silicon also significantly improves the hardness and thus wear-resistance of aluminum.[16] Silicon is an important constituent of electrical steel, modifying its resistivity and ferromagnetic properties.

Metallurgical grade silicon is silicon of 95–99% purity. About 55% of the world consumption of metallurgical purity silicon goes for production of aluminum-silicon alloys for aluminum part casts, mainly for use in the automotive industry. The reason for the high silicon use in these alloys is noted above.[17] Much of the rest of metallurgical-grade silicon is used by the chemical industry for production of the important industrial product fumed silica. The remainder is used in production of other fine chemicals such as silanes and some types of silicones.


Electronics
Since most elemental silicon produced remains as ferrosilicon alloy, only a relatively small amount (20%) of the elemental silicon produced is refined to metallurgical grade purity (a total of 1.3–1.5 million metric tons/year). The fraction of silicon metal which is further refined to semiconductor purity is estimated at only 15% of the world production of metallurgical grade silicon.[17] However, the economic importance of this small very high-purity fraction (especially the ~ 5% which is processed to monocrystalline silicon for use in integrated circuits) is disproportionately large.
Pure monocrystalline silicon is used to produce silicon wafers used in the semiconductor industry, in electronics and in some high-cost and high-efficiency photovoltaic applications. In terms of charge conduction, pure silicon is an intrinsic semiconductor which means that unlike metals it conducts electron holes and electrons which may be released from atoms within the crystal by heat, and thus increase silicon's electrical conductivity with higher temperatures. Pure silicon has too low a conductivity (i.e., too high a resistivity) to be used as a circuit element in electronics. In practice, pure silicon is doped with small concentrations of certain other elements, a process that greatly increases its conductivity and adjusts its electrical response by controlling the number and charge (positive or negative) of activated carriers. Such control is necessary for transistors, solar cells, semiconductor detectors and other semiconductor devices, which are used in the computer industry and other technical applications. For example, in silicon photonics, silicon can be used as a continuous wave Raman laser medium to produce coherent light, though it is ineffective as an everyday light source.

In common integrated circuits, a wafer of monocrystalline silicon serves as a mechanical support for the circuits, which are created by doping, and insulated from each other by thin layers of silicon oxide, an insulator which is easily produced by exposing the element to oxygen under the proper conditions. Silicon has become the most popular material to build both high power semiconductors and integrated circuits. The reason is that silicon is the semiconductor that can withstand the highest temperatures and electrical powers without becoming dysfunctional due to avalanche breakdown (a process in which an electron avalanche is created by a chain reaction process whereby heat produces free electrons and holes, which in turn produce more current which produces more heat). In addition, the insulating oxide of silicon is not soluble in water, which gives it an advantage over germanium (an element with similar properties which can also be used in semiconductor devices) in certain type of fabrication techniques.

Monocrystalline silicon is expensive to produce, and is usually only justified in production of integrated circuits, where tiny crystal imperfections can interfere with tiny circuit paths. For other uses, other types of pure silicon which do not exist as single crystals may be employed. These include hydrogenated amorphous silicon and upgraded metallurgical-grade silicon (UMG-Si) which are used in the production of low-cost, large-area electronics in applications such as liquid crystal displays, and of large-area, low-cost, thin-film solar cells. Such semiconductor grades of silicon which are either slightly less pure than those used in integrated circuits, or which are produced in polycrystalline rather than monocrystalline form, make up roughly similar amount of silicon as are produced for the monocrystalline silicon semiconductor industry, or 75,000 to 150,000 metric tons per year. However, production of such materials is growing more quickly than silicon for the integrated circuit market. By 2013 polycrystalline silicon production, used mostly in solar cells, is projected to reach 200,000 metric tons per year, while monocrystalline semiconductor silicon production (used in computer microchips) remains below 50,000 tons/year.

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Mass number..

Mass number

The mass number (A), also called atomic mass number or nucleon number, is the total number of protons and neutrons (together known as nucleons) in an atomic nucleus.
Because protons and neutrons both are baryons, the mass number A is identical with the baryon number B as of the nucleus as of the whole atom or ion.
The mass number is different for each different isotope of a chemical element. This is not the same as the atomic number (Z) which denotes the number of protons in a nucleus, and thus uniquely identifies an element.
Hence, the difference between the mass number and the atomic number gives the number of neutrons (N) in a given nucleus: N=A−Z.

The mass number is written either after the element name or as a superscript to the left of an element's symbol. For example, the most common isotope of carbon is carbon-12, or ¹² ;C, which has 6 protons and 6 neutrons. The full isotope symbol would also have the atomic number (Z) as a subscript to the left of the element symbol directly below the mass number: ¹²₆C. This is technically redundant, as each element is defined by its atomic number, so it is often omitted.

See the image below.

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Atomic number.

• In chemistry and physics, the atomic number (also known as the proton number) is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus.

• It is conventionally represented by the symbol Z.

• The atomic number uniquely identifies a chemical element. In an atom of neutral charge, the atomic number is also equal to the number of electrons.

• See the image below for  easy understanding.

 

 

 

 

extra:
The atomic number, Z, should not be confused with the mass number, A, which is the number of nucleons, the total number of protons and neutrons in the nucleus of an atom.
The number of neutrons, N, is known as the neutron number of the atom; thus, A = Z + N. Since protons and neutrons have approximately the same mass (and the mass of the electrons is negligible for many purposes), and the mass defect is usually very small compared to the mass, the atomic mass of an atom is roughly equal to A.


The conventional symbol Z comes from the German word Zahl meaning number/numeral/figure, which prior to the modern synthesis of ideas from chemistry and physics, merely denoted an element's numerical place in the periodic table. Only after 1915, with the suggestion and evidence that this Z number was also the nuclear charge and a physical characteristic of atoms, did the word Atomzahl and its English equivalent atomic number come into common use.

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What is a atom (Definition)

Atom Definition:
An atom is the defining structure of an element, which cannot be broken by any chemical means. A typical atom consists of a nucleus of protons and neutrons with electrons orbiting this nucleus.

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Chemistry simple definitions A to Z arranged

Chemistry simple definitions A to Z



Absolute Entropy (of a substance)
    The increase in the entropy of a substance as it goes from a perfectly ordered crystalline form at 0 °K (where its entropy is zero) to the temperature in question.

Absolute Zero
    The zero point on the absolute temperature scale; -273.15°C or 0 K; theoretically, the temperature at which molecular motion ceases.

Absorption Spectrum
    Spectrum associated with absorption of electromagnetic radiation by atoms (or other species) resulting from transitions from lower to higher energy states.

Accuracy
    How closely a measured value agrees with the correct value.

Acid
    A substance that produces H+(aq) ions in aqueous solution. Strong acids ionize completely or almost completely in dilute aqueous solution. Weak acids ionize only slightly.

Acid Anhydride
    The oxide of a nonmetal that reacts with water to form an acid.

Acid Anhydride
    Compound produced by dehydration of a carbonic acid; general formula is R--C--O--C--R

Acidic Salt
    A salt containing an ionizable hydrogen atom; does not necessarily produce acidic solutions.

Activation Energy
    Amount of energy that must be absorbed by reactants in their ground states to reach the transition state so that a reaction can occur.

Active Metal
    Metal with low ionization energy that loses electrons readily to form cations.

Activity (of a component of ideal mixture)
    A dimensionless quantity whose magnitude is: equal to molar concentration in an ideal solution; equal to partial pressure in an ideal gas mixture; and defined as 1 for pure solids or liquids.

Activity Series
    A listing of metals (and hydrogen) in order of decreasing activity

Actual Yield
    Amount of a specified pure product actually obtained from a given reaction. Compare with Theoretical Yield.

Actinides
    Elements 90 to 103 (after actinium)

Acyl Group
    Compound derived from a carbonic acid by replacing the --OH group with a halogen (X), usually --Cl; general formula is O R--C--X

Addition Reaction
    A reaction in which two atoms or groups of atoms are added to a molecule, one on each side of a double or triple bond

Adhesive Forces
    Forces of attraction between a liquid and another surface.

Adsorption
    Adhesion of a species onto the surfaces of particles

Alcohol
    Hydrocarbon derivative containing an --OH group attached to a carbon atom not in an aromatic ring.

Aldehyde
    Compound in which an alkyl or aryl group and a hydrogen atom are attached to a carbonyl group and a hydrogen atom are attached to a carbonyl group; general formula, O-R-C-H

Alkali Metals
    Metals of Group IA (Na, K, Rb).

Alkaline Battery
    A dry cell in which the electrolyte contains KOH.

Alkaline Earth Metals
    Group IIA metals

Alkenes (Olefins)
    Unsaturated hydrocarbons that contain one or more carbon-carbon double bonds.

Alkyl Group
    A group of atoms derived from an alkane by the removal of one hydrogen atom.

Alkylbenzene
    A compound containing an alkyl group bonded to a benzene ring.

Alkynes
    Unsaturated hydrocarbons that contain one or more carbon-carbon triple bonds.

Allotropes
    Different forms of the same element in the same physical state.

Allotropic Modifications (Allotropes)
    Different forms of the same element in the same physical state.

Alloying
    Mixing of metal with other substances (usually other metals) to modify its properties.

Alpha Particle
    A helium nucleus.

Alpha (a) Particle
    Helium ion with 2+ charge; an assembly of two protons and two neutrons.

Alums
    Hydrated sulfates of the general formula M+M3+(SO4)2.12H2).

Amide
    Compound containing the O-C-N group.
    Compound that can be considered a derivative of ammonia in which one or more hydrogens are replaced by a alkyl or aryl groups.

Amine
    Derivatives of ammonia in which one or more hydrogen atoms have been replaced by organic groups.

Amine Complexes
    Complex species that contain ammonia molecules bonded to metal ions.

Amino Acid
    Compound containing both an amino and a carboxylic acid group.The --NH2 group.
    For more information see:Amino Acids

Amorphous Solid
    A noncrystalline solid with no well-defined ordered structure.

Ampere
    Unit of electrical current; one ampere equals one coulomb per second.

Amphiprotism
    Ability of a substance to exhibit amphiprotism by accepting donated protons.

Amphoterism
    The ability to react with both acids and bases.
    Ability of substance to act as either an acid or a base.

Anion
    A negative ion; an atom or goup of atoms that has gained one or more electrons.

Anode
    In a cathode ray tube, the positive electrode.
    Electrode at which oxidation occurs.

Antibonding Orbital
    A molecular orbital higher in energy than any of the atomic orbitals from which it is derived; lends instability to a molecule or ion when populated with electrons; denoted with a star (*) superscript or symbol.

Aromatic Hydrocarbons
    Benzene and its derivatives.

Artificial Transmutation
    An artificially induced nuclear reaction caused by the bombardment of a nucleus with subatomic particiles or small nucei.

Aryl Group
    Group of atoms remaining after a hydrogen atom is removed from the aromatic system.

Associated Ions
    Short-lived species formed by the collision of dissolved ions of opposite charges.

Atmosphere
    A unit of pressure; the pressure that will support a column of mercury 760 mm high at 0 °C.

Atom
    The smallest particle of an element

Atomic Mass Unit (amu)
    One twelfth of a mass of an atom of the carbon-12 isotope; a unit used for stating atomic and formula weights; also called dalton.

Atomic Number
    Integral number of protons in the nucleus; defines the identity of element.

Atomic Orbital
    Region or volume in space in which the probability of finding electrons is highest.

Atomic Radius
    Radius of an atom.

Atomic Weight
    Weighted average of the masses of the constituent isotopes of an element; The relative masses of atoms of different elements.

Aufbau ('building up') Principle
    Describes the order in which electrons fill orbitals in atoms.

Autoionization
    An ionization reaction between identical molecules.

Avogadro's Law
    At the same temperature and pressure, equal volumes of all gases contain the same number of molecules.

Avogadro's Number
    The number (6.022x 10²³) of atoms, molecules or particles found in exactly 1 mole of substance.

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Background Radiation
    Ratiation extraneous to an experiment. Usually the low-level natural radiation form cosmic rays and trace radioactive substances present in our environment.

Band
    A series of very closely spaced, nearly continuous molecular orbitals that belong to the crystal as a whole.

Band of Stability
    Band containing nonradioactive nuclides in a plot of number of neutrons versus atomic number.

Band Theory of Metals
    Theory that accounts for the bonding and properties of metallic solids.

Barometer
    A device for measuring pressure.

Base
    A substance that produces OH (aq) ions in aqueous solution. Strong soluable bases are soluble in water and are completely dissociated. Weak bases ionize only slightly.

Basic Anhydride
    The oxide of a metal that reacts with water to form a base.

Basic Salt
    A salt containing an ionizable OH group.

Beta Particle
    Electron emitted from the nucleus when a neuton decays to a proton and an electron.

Biodegradability
    The ability of a substance to be broken down into simpler substances by bacteria.

Binary Acid
    A binary compound in which H is bonded to one or more of the more electronegative nonmetals.

Binary Compound
    A compound consisting of two elements; may be ionic or covalent.

Binding Energy (nuclear binding energy)
    The energy equivalent (E = mc^2) of the mass deficiency of an atom.
    where: E = is the energy in joules, m is the mass in kilograms, and c is the speed of light in m/s^2

Boiling Point
    The temperature at which the vapor pressure of a liquid is equal to the applied pressure; also the condensation point

Boiling Point Elevation
    The increase in the boiling point of a solvent caused by the dissolution of a nonvolatile solute.

Bomb Calorimeter
    A device used to measure the heat transfer between system and surroundings at constant volume.
    For more information see Analytical Chemistry

Bond Energy
    The amount of energy necessary to break one mole of bonds of a given kind (in gas phase).
    The amount of energy necessary to break one mole of bonds in a substance, dissociating the sustance in the gaseous state into atoms of its elements in the gaseous state.

Bond Order
    Half the numbers of electrons in bonding orbitals minus half the number of electrons in antibonding orbitals.

Bonding Orbital
    A molecular orbit lower in energy than any of the atomic orbitals from which it is derived; lends stability to a molecule or ion when populated with electron

Bonding Pair
    Pair of electrons involved in a covalent bond.

Boron Hydrides
    Binary compounds of boron and hydrogen.

Born-Haber Cycle
    A series of reactions (and accompanying enthalpy changes) which, when summed, represents the hypothetical one-step reaction by which elements in their standard states are converted into crystals of ionic compounds (and the accompanying enthalpy changes.)

Boyle's Law
    At constant temperature the volume occupied by a definite mass of a gas is inversely proportional to the applied pressure.

Breeder Reactor
    A nuclear reactor that produces more fissionable nuclear fuel than it consumes.

Bronsted-Lowry Acid
    A proton donor.

Bronsted-Lowry Base
    A proton acceptor

Buffer Solution
    Solution that resists change in pH; contains either a weak acid and a soluble ionic salt of the acid or a weak base and a soluble ionic salt of the base.

Buret
    A piece of volumetric glassware, usually graduated in 0.1-mL intervals, that is used to deliver solutions to be used in titrations in a quantitative (dropwise) manner.

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Calorie
    The amount of heat required to raise the temperature of one gram of water from 14.5°C to 15.5°C. 1 calorie = 4.184 joules.

Calorimeter
    A device used to measure the heat transfer between system and surroundings.
    For further information see Analytical Chemistry

Canal Ray
    Stream of positively charged particles (cations) that moves toward the negative electrode in cathode ray tubes; observed to pass through canals in the negative electrode.

Capillary
    A tube having a very small inside diameter.

Capillary Action
    The drawing of a liquid up the inside of a small-bore tube when adhesive forces exceed cohesive forces, or the depression of the surface of the liquid when cohesive forces exceed the adhesive forces.

Carbanion
    An organic ion carrying a negative charge on a carbon atom.

Carbonium ion
    An orgainic ion carrying a positive charge on a carbon atom.

Carcinogen
    A substance capable of causing or producing cancer in mammals.

Catalyst
    A substance that speeds up a chemical reaction without being consumed itself in the reaction.
    A substance that alters (usually increases) the rate at which a reaction occurs.

Catenation
    Bonding of atoms of the same element into chains or rings.
    The bonding together of atoms of the same element to form chains.
    The ability of an element to bond to itself.

Cathode
    Electrode at which reduction occurs
    In a cathode ray tube, the negative electrode.

Cathodic Protection
    Protection of a metal (making ir a cathode) against corrosion by attaching it to a sacrifical anode of a more easily oxidized metal.

Cathode Ray Tube
    Closed glass tube containing a gas under low pressure, with electrodes near the ends and a luminescent screen at the end near the positive electrode; produces cathode rays when high voltage is applied.

Cation
    A positive ion; an atom or group of atoms that has lost one or more electrons.

Cell Potential
    Potential difference, Ecell, between oxidation and reduction half-cells under nonstandard conditions.

Central Atom
    An atom in a molecule or polyatomic ion that is bonded to more than one other atom.

Chain Reaction
    A reaction that, once initiated, sustains itself and expands.
    This is a reaction in which reactive species, such as radicals, are produced in more than one step. These reactive species, radicals, propagate the chain reaction.

Chain Termination Step
    The combination of two radicals, which removes the reactive species that propagate the change reaction.

Charle's Law
    At constant pressure the volume occupied by a definite mass of gas is directly proportional to its absolute temperature.

Chemical Bonds
    The attractive forces that hold atoms together in elements or compounds.

Chemical Change
    A change in which one or more new substances are formed.

Chemical Equation
    Description of a chemical reaction by placing the formulas of the reactants on the left and the formulas of products on the right of an arrow.

Chemical Equilibrium
    A state of dynamic balance in which the rates of forward and reverse reactions are equal; there is no net change in concentrations of reactants or products while a system is at equilibrium.

Chemical Hygiene Officer (CHO)
    A person or employee who is qualified by training or experience to provide technical guidance in the development and implementations of the provisions of a Chemical Hygiene Plan (CHP)

Chemical Hygiene Plan (CHP)
    A written program developed and implemented by an employer designating proceedures, equipment, personal protective equipment, and work practices that are capable of protecting employees from the health hazards presented by hazardous chemicals usid in that particular workplace.

Chemical Kinetics
    The study of rates and mechanisms of chemical reactions and of the factors on which they depend.

Chemical Periodicity
    The variations in properties of elements with their position in the periodic table

Cis-
    The prefix used to indicate that groups are located on the same side of a bon about which rotation is restricted.

Cis-Trans Isomerism
    A type of geometrical isomerism related to the angles between like ligands.

Clay
    A class of silicate and aluminosilicate minerals with sheet-like structures that have enormous surface areas that can absorb large amounts of water.

Cloud Chamber
    A device for observing the paths of speeding particiles as vapor molecules condense on them to form foglike tracks.

Coefficient of expansion
    The ratio of the change in length or volumen of a body to the original lengthor volume for a unit change in temperature.

Cohesive Forces
    All the forces of attraction among particles of a liquid.

Coke
    An impure form of carbon obtained by destructive distillation of coal or petroleum.

Colligative Properties
    Physical properties of solutions that depend upon the number but not the kind of solute particles present.

Collision Theory
    Theory of reaction rates that states that effective collisions between reactant molecules must occur in order for the reaction to occur.

Colloid
    A heterogeneous mixture in which solute-like particles do not settle out.

Combination Reaction
    Reaction in which two substances ( elements or compounds ) combine to form one compound.
    Reaction of a substance with oxygen in a highly exothermic reaction, usually with a visible flame.

Combustible
    Classification of liquid substances that will burn on the basis of flash points. A combustible liquid means any liquid having a flash point at or above 37.8°C (100°F) but below 93.3°C (200°F), except any mixture having components with flash points of 93.3°C (200°F) or higher, the total of which makes up 99 percent or more of the total volume of the mixture.

Common Ion Effect
    Suppression of ionization of a weak electrolyte by the presence in the same solution of a strong electrolyte containing one of the same ions as the weak electrolyte.

Complex Ions
    Ions resulting from the formation of coordinate covalent bonds between simple ions and other ions or molecules.

Composition Stoichiometry
    Descibes the quantitative (mass) relationships among elements in compounds.

Compound
    A substance of two or more elements in fixed proportions. Compounds can be decomposed into their constituent elements.
    For more Information see Compounds

Compressed Gas
    A gas or mixture of gases having, in a container an absolute pressure exceeding 40 psi at 21.1°C (70°F)
    A gass or mixture having in a container, an absolute pressure exceeding 104 psi at 54.4°C (130°F) regardless of the pressure at (21.1°C (70°F)
    A liquid having a vapour pressure exceeding 40 psi at 37.8°C (70°F) as determined by ASTM D-323-72.

Concentration
    Amount of solute per unit volume or mass of solvent or of solution.

Condensation
    Liquefaction of vapor.

Condensed Phases
    The liquid and solid phases; phases in which particles interact strongly.

Condensed States
    The solid and liquid states.

Conduction Band
    A partially filled band or a band of vacant energy levels just higher in energy than a filled band; a band within which, or into which, electrons must be promoted to allow electrical conduction to occur in a solid.

Conjugate Acid-base Pair
    In Bronsted-Lowry terminology, a reactant and product that differ by a proton, H+.

Conformations
    Structures of a compound that differ by the extent of rotation about a single bond.

Continuous Spectrum
    Spectrum that contains all wave-lengths in a specified region of the electromagnetic spectrum.

Control Rods
    Rods of materials such as cadmium or boron steel that act as neutron obsorbers (not merely moderaters) used in nuclear reactors to control neutron fluxes and therfore rates of fission.

Conjugated Double Bonds
    Double bonds that are separated from each other by one single bond -C=C-C=C-.

Contact Process
    Industrial process by which sulfur trioxide and sulfuric acid are produced from sulfur dioxide.

Coordinate Covalent Bond
    Covalent bond in which both shared electrons are furnished by the same species; bond between a Lewis acid and Lewis base.

Coordinate Covalent Bond
    A covalent bond in which both shared electrons are donated by the same atom; a bond between a Lewis base and a Lewis acid.

Coordination Compound or Complex
    A compound containing coordinate covalent bonds.

Coordination Isomers
    Isomers involving exchanges of ligands between complex cation and complex anion of the same compound.

Coordination Number
    In describing crystals, the number of nearest neighbours of an atom or ion.
    The number of donor atoms coordinated to a metal.

Coordination Sphere
    The metal ion and its coordinating ligands but not any uncoordinated counter-ions.

Corrosion
    Oxidation of metals in the presence of air and moisture.
    For more information see Corrosion

Coulomb
    Unit of electrical charge.

Coulometry
    The quantitative application of Faraday's Law to the analysis of materials. The current and time are the usual variables measured.

Covalent Bond
    Chemical bond formed by the sharing of one or more electron pairs between two atoms.

Covalent Compounds
    Compounds containing predominantly covalent bonds.

Critical Mass
    The minimum mass of a particular fissionable nuclide in a given volume required to sustain a nuclear chain reaction.

Critical Point
    The combination of critical temperature and critical pressure of a substance.

Critical Pressure
    The pressure required to liquefy a gas (vapor) at its critical temperature.

Critical Temperature
    The temperature above which a gas cannot be liquefied; the temperature above which a substance cannot exhibit distinct gas and liquid phases.

Crystal Field Stabilization Energy
    A measure of the net energy of stabilization gained by a metal ion's nonbonding d electrons as a result of complex formation.
    For more information see Crystallography

Crystal Field Theory
    Theory of bonding in transition metal complexes in which ligands and metal ions are treated as point charges; a purely ionic model; ligand point charges represent the crystal (electrical) field perturbing the metal?s d orbitals containing nonbonding electrons.
    For more information see Crystallography

Crystal Lattice
    A pattern of arrangement of particles in a crystal.
    For more information see Crystallography

Crystal Lattice Energy
    Amount of energy that holds a crystal together; the energy change when a mole of solid is formed from its constituent molecules or ions (for ionic compounds) in their gaseous state.
    The energy charge when one mole of formula units of a crystalline solid is formed from its ions, atoms, or molecules in the gas phase; always negative.
    For more information see Crystallography

Crystalline Solid
    A solid characterized by a regular, ordered arrangement of particles.
    For more information see Crystallography

Curie (Ci)
    The basic unit used to describe the intensity of radioactivity in a sample of material. One curie equals 37 billion disintegrations per second or approximately the amount of radioactivty given off by 1 gram of radium.

Cyclotron
    A device for accelerating charged particles along a spiral path.

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Daughter Nuclide
    Nuclide that is produced in a nuclear decay.

Debye
    The unit used to express dipole moments.

Degenerate
    Of the same energy.

Delocalization
    Of electrons; refers to bonding electrons that are distributed among more than two atoms that are bonded together; occurs in species that exhibit resonance.
    The formation of a set of molecular orbitals that extend over more than two atoms; important in species that valence bond theory describes in terms of resonance.

Denaturation
    A process pertaining to a change in structure of a protein form regular to irregular arrangement of the polypeptide chains.

Denatured
    A commercial term used to describe ethanol that has been rendered unfit for human consumption because of the addition of harmful ingredients to make it sales tax-expempt.

Density
    Mass per unit Volume: D=MV

Deposition
    The direct solidification of a vapor by cooling; the reverse of sublimation.

Derivative
    A compound that can be imagined to arise from a partent compound by replacement of one atom with another atom or group of atoms. Used extensively in orgainic chemistry to assist in identifying compounds.

Dermal toxicity
    Adverse health effects resulting from skin exposure ot a substance.

Designated area
    An area that may be used for work with carcinogens, reproductive toxins, or substances that have a high degree of acute toxicity. A designated area may be the entire laboratory, an area of a laboratory, or a device such as a loboratory hood.

Detergent
    A soap-like emulsifer that contains a sulfate, SO3 or a phosphate group instead of a carboxylate group.

Deuterium
    An isotope of hydrogen whose atoms are twice as massive as ordinary hydrogen;deuterion atoms contain both a proton and a neutron in the nucleus.

Dextrorotatory
    Refers to an optically active substance that rotates the plane of plane polarized light clockwise; also called dextro.

Diagonal Similarities
    Refers to chemical similarities in the Periodic Table of elements of Period 2 to elements of Period 3 one group to the right; especially evident toward the left of the periodic table.

Diamagnetism
    Weak repulsion by a magnetic field.

Differential Scanning Calorimetry (DSC)
    A technique for measuring the temperature, direction, and magnitude of thermal transitions in a sample material by heating/cooling and comparing the amount of energy required to maintain its rate of temperature increase or decrease with an inert reference material under similar conditions.

Differential Thermal Analysis (DTA)
    A technique for observing the temperature, direction, and magnitude of thermally induced transitions in a material by heating/cooling a sample and comparing its temperature with that of an inert reference material under similar conditions.

Differential Thermometer
    A thermometer used for accurate measurement of very small changes in temperature.

Dilution
    Process of reducing the concentration of a solute in solution, usually simply by mixing with more solvent.

Dimer
    Molecule formed by combination of two smaller (identical) molecules.

Dipole
    Refers to the separation of charge between two covalently bonded atoms

Dipole-dipole Interactions
    Attractive interactions between polar molecules, that is, between molecules with permanent dipoles.

Dipole Moment
    The product of the distance separating opposite charges of equal magnitude of the charge; a measure of the polarity of a bond or molecule; a measured dipole moment refers to the dipole moment of an entire molecule.

Dispersing Medium
    The solvent-like phase in a colloid.

Dispersed Phase
    The solute-like species in a colloid.

Displacement Reactions
    Reactions in which one element displaces another from a compound.

Disproportionation Reactions
    Redox reactions in which the oxidizing agent and the reducing agent are the same species.

Dissociation
    In aqueous solution, the process in which a solid ionic compound separates into its ions.

Dissociation Constant
    Equilibrium constant that applies to the dissociation of a comples ion into a simple ion and coordinating species (ligands).

Distilland
    The material in a distillation apparatus that is to be distilled.

Distillate
    The material in a distillation apparatus that is collected in the receiver.

Distillation
    The separation of a liquid mixture into its components on the basis of differences in boiling points.
    The process in which components of a mixture are separated by boiling away the more volitile liquid.

Domain
    A cluster of atoms in a ferromagnetic substance, all of which align in the same direction in the presence of an external magnetic field.

Donor Atom
    A ligand atom whose electrons are shared with a Lewis acid.

D-Orbitals
    Beginning in the third energy level, aset of five degenerate orbitals per energy level, higher in energy than s and p orbitals of the same energy level.

Dosimeter
    A small, calibrated electroscope worn by laboratory personnel and designated to detect and measure incident ionizing radiation or chemical exposure.

Double Bond
    Covalent bond resulting from the sharing of four electrons (two pairs) between two atoms.

Double Salt
    Solid consisting of two co-crystallized salts.

Doublet
    Two peaks or bands of about equal intensity appearing close together on a spectrogram.

Downs Cell
    Electrolytic cell for the commercial electrolysis of molten sodium chloride.
    For further information see Electrochemistry or Fuel Cells

DP number
    The degree of polymerization; the average number of monomer units per polymer unit.

Dry Cells
    Ordinary batteries (voltaic cells) for flashlights. radios, and so on; many are Leclanche cells.
    For further information see Electrochemistry or Fuel Cells

D -Transition elements (metals)
    B Group elements except IIB in the periodic table; sometimes called simply transition elements EX. Fe, Ni, Cu, Ti .
    For further information see Metals

Dumas Method
    A method used to determine the molecular weights of volatile liquids.

Dynamic Equilibrium
    An equilibrium in which processes occur continuously, with no net change.
    When two (or more) processes occur at the same rate so that no net change occurs.

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Effective Collisons
    Collision between molecules resulting in a reaction; one in which the molecules collide with proper relative orientations and sufficient energy to react.

Effective Molality
    The sum of the molalities of all solute particles in a solution.

Effective Nuclear Charge
    The nuclear charge experienced by the outermost electrons of an atom; the actual nuclear charge minus the effects of shielding due to inner-shell electrons.
    Example: Set of dx2-y2 and dz2 orbitals; those d orbitals within a set with lobes directed along the x-, y-, and z-axes.

Electrical Conductivity
    Ability to conduct electricity.

Electrochemistry
    Study of chemical changes produced by electrical current and the production of electricity by chemical reactions.

Electrodes
    Surfaces upon which oxidation and reduction half-reactions; occur in electrochemical cells.

Electrode Potentials
    Potentials, E, of half-reactions as reductions versus the standard hydrogen electrode.

Electrolysis
    Process that occurs in electrolytic cells.

Electrolyte
    A substance whose aqueous solutions conduct electricity.

Electrolytic Cells
    Electrochemical cells in which electrical energy causes nospontaneous redox reactions to occur.
    An electrochemical cell in which chemical reactions are forced to occur by the application of an outside source of electrical energy.

Electrolytic Conduction
    Conduction of electrical current by ions through a solution or pure liquid.

Electromagnetic Radiation
    Energy that is propagated by means of electric and magnetic fields that oscillate in directions perpendicular to the direction of travel of the energy.

Electromotive Series
    The relative order of tendencies for elements and their simple ions to act as oxidizing or reducing agents; also called the activity series.

Electron
    A subatomic particle having a mass of 0.00054858 amu and a charge of 1-.

Electron Affinity
    The amount of energy absorbed in the process in which an electron is added to a neutral isolated gaseous atom to form a gaseous ion with a 1- charge; has a negative value if energy is released.

Electron Configuration
    Specific distribution of electrons in atomic orbitals of atoms or ions.

Electron Deficient Compounds
    Compounds that contain at least one atom (other than H) that shares fewer than eight electrons

Electronic Transition
    The transfer of an electron from one energy level to another.

Electronegativity
    A measure of the relative tendency of an atom to attract electrons to itself when chemically combined with another atom.

Electronic Geometry
    The geometric arrangement of orbitals containing the shared and unshared electron pairs surrounding the central atom of a molecule or polyatomic ion.

Electrophile
    Positively charged or electron-deficient.

Electrophoresis
    A technique for separation of ions by rate and direction of migration in an electric field.

Electroplating
    Plating a metal onto a (cathodic) surface by electrolysis.

Element
    A substance that cannot be decomposed into simpler substances by chemical means.

Eluant or eluent
    The solvent used in the process of elution, as in liquid chromatography.

Eluate
    Solvent (or mobile phase) which passes through a chromatographic column and removes the sample components from the stationary phase.

Emission Spectrum
    Spectrum associated with emission of electromagnetic radiation by atoms (or other species) resulting from electronic transitions from higher to lower energy states.

Emulsifying Agent
    A sustance that coats the particles of the dispersed phase and prevents coagulation of colloidal particles; an emulsifier.

Emulsion
    Colloidal suspension of a liquid in a liquid.

Enantiomer
    One of the two mirror-image forms of an optically active molecule.

Endothermic
    Describes processes that absorb heat energy.

Endothermicity
    The absorption of heat by a system as the process occurs.

End Point
    The point at which an indicator changes colour and a titration is stopped.

Energy
    The capacity to do work or transfer heat.

Enthalpy
    The heat content of a specific amount of substance; defined as E= PV.

Entropy
    A thermodynamic state or property that measures the degree of disorder or randomness of a system.
    For more information see Thermochemistry

Enzyme
    A protein that acts as a catalyst in biological systems.

Equation of State
    An equation that describes the behavior of matter in a given state; the van der Waals equation describes the behavior of the gaseous state.

Equilibrium or Chemical Equilibrium
    A state of dynamic balance in which the rates of forward and reverse reactions are equal; the state of a system when neither forward or reverse reaction is thermodynamically favored.

Equilibrium Constant
    A quantity that characterizes the position of equilibrium for a reversible reaction; its magnitude is equal to the mass action expression at equilibrium. K varies with temperature.

Equivalence Point
    The point at which chemically equivalent amounts of reactants have reacted.

Equivalent Weight
    An oxidizing or reducing agent, who's mass gains (oxidizing agents) or loses (reducing agents) 6.022 x 1023 electrons in a redox reaction.
    The mass of an acid or base that furnishes or reacts with 6.022 x 1023 H3O+ or OH- ions.

Essential Oil
    A plant extract that has a distinctive odour or flavour.

Ester
    A Compound of the general formula R-C-O-R1 where R and R1 may be the same or different, and may be either aliphatic or aromatic.

Ether
    Compound in which an oxygen atom is bonded to two alkyl or two aryl groups, or one alkyl and one aryl group.

Eutrophication
    The undesirable overgrowth of vegetation caused by high concentrates of plant nutrients in bodies of water.

Evaporization
    Vaporization of a liquid below its boiling point.

Evaporation Rate
    The rate at which a particular substance will vapourize (evaporate) when compared to the rate of a known substance such as ethyl ether. This term is especially useful for health and fire-hazard considerations.

Excited State
    Any state other than the ground state of an atom or molecule.

Exothermic
    Describes processes that release heat energy.

Exothermicity
    The release of heat by a system as a process occurs.

Explosive
    A chemical or compound that causes a sudden, almost instantaneous release or pressure, gas, heat and light when subjected to sudden shock, pressure, high temperature or applied potential.

Explosive limits
    The range of concentrations over which a flammable vapour mixed with proper ratios of air will ignite or explode if a source of ignitions is provided.

Extensive Property
    A property that depends upon the amount of material in a sample.

Extrapolate
    To estimate the value of a result outside the range of a series of known values. Technique used in standard additions calibration procedure.

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Faraday
    One faraday of electricity corresponds to the charge on 6.022 x 10 23 electrons, or 96,487 coulombs.

Faraday's Law of Electrolysis
    One equivalent weight of a substance is produced at each electrode during the passage of 96,487 coulombs of charge through an electrolytic cell.

Fast Neutron
    A neutron ejected at high kinetic energy in a nuclear reaction.

Fat
    Solid triester of glycerol and (mostly) saturated fatty acids.

Fatty Acids
    An aliphatic acid; many can obtained from animal fats.

Ferromagnetism
    The ability of a substance to become permanently magnetized by exposure to an external magnetic field.

Film badge
    A small patch of photographic film worn on clothing to detect and measure accumulated incident ionizing radiation.

Flammable
    A liquid as defined by NFPD and DOT as having a flash point below 37.8°C (100°F).

Flash Point
    The temperature at which a liquid will yield enough flamable vapour to ignite. There are various recognized industrial testing methods; therefore the method used must be stated.

Fluorescence
    Absorption of high energy radiation by a substance and subsequent emission of visible light.

Fossil Fuels
    Substances consisting largely of hydrocarbons, derived from decay of organic materials under geological conditions of high pressure and temperature (metamorphism) include coal, petroleum, natural gas, peat and oil shale.
    For further information see Fuel Chemistry

Frasch Process
    Method by which elemental sulfur is mined or extracted. Sulfur is melted with superheated water (at 170°C under high pressure) and forced to the surface of the earth as a slurry.

First Law of Thermodynamics
    The total amount of energy in the universe is constant (also known as the Law of Conservation of Energy) energy is neither created nor destroyed in ordinary chemical reactions and physical changes.
    For further information see Thermochemistry

Flotation
    Method by which hydrophobic (water-repelling) particles of an ore are separated from hydrophilic (water-attracting) particles of a metallurgical pretreatment process.

Fluids
    Substances that flow freely; gases and liquids.

Flotation

Flux
    A substance added to react with the charge, or a product of its reduction, in metallurgy; usually added to lower a melting point.

Foam
    Colloidal suspension of a gas in a liquid.

Forbidden Zone
    A relatively large energy separation between an insulator's highest filled electron energy band and the next higher energy vacant band. Beginning in the fourth energy level, a set of seven degenerate orbitals per energy level, higher in energy than s, p, and d orbitals of the same energy level.

Formal Charge
    A method of counting electrons in a covalently bonded molecule or ion; counts bonding electrons as though they were equally shared between the two atoms.

Formula
    Combination of symbols that indicates the chemical composition of a substance.

Formula Unit
    The smallest repeating unit of a substance. The molecule for nonionic substances

Formula Weight
    The mass of one formula unit of a substance in atomic mass units.

Fractional Distillation
    The process in which a fractioning column is used in distillation apparatus to separate components of a liquid mixture that have different boiling points.

Fractional Precipitation
    Removal of some ions from solution by precipitation while leaving other ions with similar properties in solution.

Free Energy, Gibbs Free Energy
    The thermodynamic state function of a system that indicates the amount of energy available for the system to do useful work at constant T and P.

Free Energy Change
    The indicator of spontaneity of a process at constnt T and P. If delta-G is negative, the process is spontaneous.

Free Radical
    A highly reactive chemical species carrying no charge and having a single unpaired electron in an orbital.

Freezing Point Depression
    The decrease in the freezing point of a solvent caused by the presence of a solute.

Frequency
    The number of repeating corresponding points on a wave that pass a given observation point per unit time.

Fuel Cells
    Voltaic cells in which the reactants (usually gases) are supplied continuously.
    A voltaic cell that converts the chemical energy of a fuel and an oxidizing agent directly into electriacl energy on a continuous basis.

Functional Group
    A group of atoms that represents a potential reaction site in an organic compound.

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Gamma Ray
    High energy electromagnetic radiation.
    A highly penetrating type of nuclear radiation similar to x-ray radiation, except that it comes from within the nucleus of an atom and has a higher energy. Energywise, very similar to cosmic ray except that cosmic rays originate from outer space.
    For more information see Electrochemistry

Galvanizing
    Placing a thin layer of zinc on a ferrous material to protect the underlying surface from corrosion.

Gangue
    Sand, rock, and other impurities surrounding the mineral of interest in an ore.

Geiger counter
    A gas filled tube which discharges electriaclly when ionizing radiation passes through it.

Gel
    Colloidal suspension of a solid dispersed in a liquid; a semirigid solid.

Gem-dimethyl group
    Two methyl groups of the same carbon atom.

Geometrical Isomers
    Compounds with different arrangements of groups on either side of a bond with restricted rotation, such as a double bond or a single bond in a ring; for example cis-trans isomers of certain alkenes.
    Stereoisomers that are not mirror images of each other; also known as position isomers.

Graham's Law
    The rates of effusion of gases are inversely proportional to the square roots of their molecular weights or densities.

Greenhouse Effect
    Trapping of heat at the surface of the earth by carbon dioxide and water vapour in the atmosphere.

Ground State
    The lowest energy state or most stable state of an atom, molecule or ion.

Group
    A vertical column in the periodic table; also called a family.
    For more information see Periodic Tables

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Haber Process
    A process for the catalyzed industrial     production of ammonia from N2 and H2 at high temperature and pressure.

Half-Cell
    Compartment in which the oxidation or reduction half-reaction occurs in a voltaic cell.

Half-Life
    The time required for half of a reactant to be converted into product(s).
    The time required for half of a given sample to undergo radioactive decay.

Half-Reaction
    Either the oxidation part or the reduction part of a redox reaction.

Halogens
    Group VIIA elements: F, Cl, Br, I

Hard Water
    Water containing Fe3+, Ca2+, and Mg2+ ions, which forms precipates with soap.

Heat
    A form of energy that flows between two samples of matter because of their differences in temperature.

Heat Capacity
    The amount of heat required to raise the temperature of a body (of any mass) one degree Celsius.

Heat of Condensation
    The amount of heat that must be removed from one gram of a vapor at it's condensation point to condense the vapour with no change in temperature.

Heat of Crystallization
    The amount of heat that must be removed from one gram of a liquid at its freezing point to freeze it with no change in temperature.

Heat of Fusion
    The amount of heat required to melt one gram of solid at its melting point with no change in temperature. Usually expressed in J/g. The molar heat of fusion is the amount of heat required to melt one mole of a solid at its melting point with no change in temperature and is usually expressed in kJ/mol.

Heat of Solution
    The amount of heat absorbed in the formation of solution that contains one mole of solute; the value is positive if heat is absorbed (endothermic) and negative if heat is released (exothermic).

Heat of Vaporization
    The amount of heat required to vaporize one gram of a liquid at its boiling point with no change in temperature. Usually expressed in J/g. The molar heat of vaporization is the amount of heat required to vaporize one mole of liquid at its boiling point with no change in temperature and usually expressed ion kJ/mol.

Heavy Water
    Water containing deuterium, a heavy isotope of hydrogen.

Heisenberg Uncertainty Principle
    It is impossible to determine accurately both the momentum and position of an electron simultaneously.

Henry's Law
    The pressure of the gas above a solution is proportional to the concentration of the gas in the solution.

Hess' Law of Heat Summation
    The enthalpy change for a reaction is the same whether it occurs in one step or a series of steps.

Heterocyclic Amine
    Amine in which the nitrogen is part of a ring.
    For further information see Heterocyclic Chemistry

Heterogeneous Catalyst
    A catalyst that exists in a different phase (solid, liquid or gas) from the reactants; a contact catalyst.

Heterogeneous Equilibria
    Equilibria involving species in more than one phase.

Heterogeneous Mixture
    A mixture that does not have uniform composition and properties throughout.

Heteronuclear
    Consisting of different elements.

High Spin Complex
    Crystal field designation for an outer orbital complex; all t2g and eg orbitals are singly occupied before any pairing occurs.

Homogeneous Catalyst
    A catalyst that exists in the same phase (solid, liquid or gas) as the reactants.
    For more information see Catalysis

Homogeneous Equilibria
    Equilibria involving only one species in a single phase. For example, all gases, all liquids or all solids.

Homogeneous Mixture
    A mixture which has uniform composition and properties throughout.

Homologous Series
    A series of compounds in which each member differs from the next by a specific number and kind of atoms.

Homonuclear
    Consisting of only one element.

Hund's Rule
    All orbitals of a given sublevel must be occupied by single electrons before pairing begins (see Aufbau Principle)

Hybridization
    Mixing a set of atomic orbitals to form a new set of atomic orbitals with the same total electron capacity and with properties and energies intermediate between those of the original unhybridized orbitals.

Hydrate
    A solid compound that contains a definite percentage of bound water.

Hydrate Isomers
    Isomers of crystalline complexes that differ in whether water is present inside or outside the coordination sphere

Hydration
    Reaction of a substance with water.

Hydration Energy
    The energy change accompanying the hydration of a mole of gase and ions.

Hydride
    A binary compound of hydrogen.

Hydrocarbons
    Compounds that contain only carbon and hydrogen.

Hydrogen Bond
    A fairly strong dipole-dipole interaction (but still considerably weaker than the covalent or ionic bonds) between molecules containing hydrogen directly bonded to a small, highly electronegative atom, such as N, O, or F.

Hydrogenation
    The reaction in which hydrogen adds across a double or triple bond.

Hydrogen-Oxygen Fuel Cell
    Fuel cell in which hydrogen is the fuel (reducing agent) and oxygen is the oxidizing agent.

Hydrolysis
    The reaction of a substance with water or its ions.

Hydrolysis Constant
    An equilibrium constant for a hydrolysis reaction.

Hydrometer
    A device used to measure the densities of liquids and solutions.

Hydrophilic Colloids
    Colloidal particles that repel water molecules.
    For more information see Colloidal Chemistry

===============================================================================


Inner Orbital Complex
    Valence bond designation for a complex in which the metal ion utilizes d orbitals for one shell inside the outermost occupied shell in its hybridization.

Isomers
    Different substances that have the same formula.

Ionization Isomers
    Isomers that result from the interchange of ions inside and outside the coordination sphere.

Inert s-pair Effect
    Characteristic of the post-transition minerals; tendency of the outermost s electrons to remain nonionized or un shared in compounds.

Insoluble Compound
    A very slightly soluble compound.

Indicators
    For acid-base titrations, organic compounds that exhibit different colors in solutions of different acidities; used to determine the point at which reaction between two solutes is complete.

Ionization Constant
    Equilibrium constant for the ionization of a weak electrolyte.

Ion Product for Water
    Equilibrium constant for the ionization of water, Kw = [H3O+][OH-] =1.00 x 10-14 at 25 °C.

Inhibitory Catalyst
    An inhibitor, a catalyst that decreases the rate of reaction.
    For more information see Catalysis

Integrated Rate Equation
    An equation giving the concentration of a reactant remaining after a specified time; has different mathematical form for different orders of reactants.

Ioniztion
    The breaking up of a compound into separate ions.

Ideal Solution
    A solution that obeys Raoult's Law exactly.

Insulator
    Poor electric and heat conductor.

Intermolecular Forces
    Forces between individual particles (atoms, molecules, ions) of a substance.

Isomorphous
    Refers to crystals having the same atomic arrangement.
    For more information see Crystallography

Ideal Gas
    A hypothetical gas that obeys exactly all postulates of the kinetic-molecular theory.

Ideal Gas Law
    The product of pressure and the volume of an ideal gas is directly proportional to the number of moles of the gas and the absolute temperature.

Ionization
    In aqueous solution, the process in which a molecular compound reacts with water and forms ions.

Ionic Bonding
    Chemical bonding resulting from the transfer of one or more electrons from one atom or a group of atoms to another.

Ionic Compunds
    Compounds containing predominantly ionic bonding.

Ionic Geometry
    The arrangement of atoms (not lone pairs of electrons) about the central atom of a polyatomic ion.

Isoelectric
    Having the same electronic configurations

Ionization Energy
    The minimum amount of energy required to remove the most loosely held electron of an isolated gaseous atom or ion.

Isotopes
    Two or more forms of atoms of the same element with different masses; atoms containing the same number of protons but different numbers of neutrons.

Ion
    An atom or a group of atoms that carries an electric charge.

==============================================================================


Joule
    A unit of energy in the SI system. One joule is 1 kg. m2/s2 which is also 0.2390 calorie. 
==============================================================================


K Capture
    Absorption of a K shell (n=1) electron by a     proton as it is converted to a neutron.

Ketone
    Compound in which a carbonyl group is bound to two alkyl or two aryl groups, or to one alkyl and one aryl group.

Kinetic Energy
    Energy that matter processes by virtue of its motion.

Kinetic-molecular Theory
    A theory, that attempts to explain macroscopic observations on gases in microscopic observations on gases in microscopic observations on gases in microscopic or molecular terms.
==============================================================================



Lanthanides
    Elements 58 to 71 (after lanthanum)

Lanthanide Contraction
    A decrease in the radii of the elements following the lanthanides compared to what would be expected if there were no f-transition metals.

Law of Combining Volumes (Gay-Lussac's Law)
    At constant temperature and pressure, the volumes of reacting gases ( and any gaseous products) can be expressed as ratios of small whole numbers;

Law of Conservation of Energy
    Energy cannot be created or destroyed; it may be changed from one form to another.

Law of Conservation of Matter
    There is no detectable change in the quantity of matter during an ordinary chemical reaction.

Law of Conservation of Matter and Energy
    The total amount of matter and energy available in the universe is fixed.

Law of Definite Proportions (Law of Constant Composition)
    Different samples of a pure compound always contain the same elements in the same proportions by mass.

Law of Partial Pressures (Dalton's Law)
    The total pressure exerted by a mixature of gases is the sum of the partial pressures of the individual gases.

Lead Storage Battery
    Secondary voltaic cell used in most automobiles.

Leclanche Cell
    A common type of dry cell.

Le Chatelier's Principle
    States that a system at equilibrium, or striving to attain equilibrium, responds in such a way as to counteract any stress placed upon it.
    If a stress (change of conditions) is applied to a system at equilibrium, the system shifts in the direction that reduces stress.

Leveling Effect
    Effect by which all acids stronger than the acid that is characteristic of the solvent react with solvent to produce that acid; similar statement applies to bases. The strongest acid (base) that can exist in a given solvent is the acid (base) characteristic of the solvent.

Levorotatory
    Refers to an optically active substance that rotates the plane of plane polarized light counterclockwise; also called levo.

Lewis Acid
    Any species that can accept a share in an electron pair.

Lewis Base
    Any species that can make available a share in an electron pair.

Lewis Dot Formula (Electron Dot Formula)
    Representation of a molecule, ion or formula unit by showing atomic symbols and only outer shell electrons

Ligand
    A Lewis base in a coordination compound.

Limiting Reactant
    Substance that stoichiometrically limits the amount of product(s) that can be formed.

Linear Accelerator
    A device used for accelerating charged particles along a straight line path.

Line Spectrum
    An atomic emission or absorption spectrum.

Linkage Isomers
    Isomers in which a particular ligand bonds to a metal ion through different donor atoms.

Liquid Aerosol
    Colloidal suspension of liquid in gas.

London Forces
    Very weak and very short-range attractive forces between short-lived temporary (induced) dipoles; also called dispersion Forces.

Lone Pair
    Pair of electrons residing on one atom and not shared by other atoms; unshared pair.

Low Spin Complex
    Crystal field designation for an inner orbital complex; contains electrons paired t2g orbitals before eg orbitals are occupied in octahedral complexes.

=================================================================================


Magnetic Quantum Number (mc)
    Quantum mechanical solu    tion to a wave equation that designates the particular orbital within a given set (s, p, d, f ) in which a electron resides.

Manometer
    A two-armed barometer.

Mass
    A measure of the amount of matter in an object. Mass is usually measured in grams or kilograms.

Mass Action Expression
    For a reversible reaction, aA + bB cC + dD the product of the concentrations of the products (species on the right), each raised to the power that corresponds to its coefficient in the balanced chemical equation, divided by the product of the concentrations of reactants (species on the left), each raised to the power that corresponds to its coefficient in the balanced chemical equation. At equilibrium the mass action expression is equal to K; at other times it is Q.[C]c[D]d [A]a[B]b = Q, or at equilibrium K

Mass Deficiency
    The amount of matter that would be converted into energy if an atom were formed from constituent particles.

Mass Number
    The sum of the numbers of protons and neutrons in an atom; an integer.

Mass Spectrometer
    An instrument that measures the charge-to-mass ratio of charged particles.
    For further information see Mass Spectrometry

Matter
    Anything that has mass and occupies space.

Mechanism
    The sequence of steps by which reactants are converted into products.

Melting Point
    The temperature at which liquid and solid coexist in equilibrium; also the freezing point.

Meniscus
    The shape assumed by the surface of a liquid in a cylindrical container.

Metal
    An element below and to the left of the stepwise division (metalloids) in the upper right corner of the periodic table; about 80% of the known elements are metals.

Metallic Bonding
    Bonding within metals due to the electrical attraction of positively charges metal ions for mobile electrons that belong to the crystal as a whole.

Metallic Conduction
    Conduction of electrical current through a metal or along a metallic surface.

Metalloids
    Elements with properties intermediate between metals and nonmetals: B, Al, Si, Ge, As, Sb, Te, Po, and At.

Metallurgy
    Refers to the overall processes by which metals are extracted from ores.

Metathesis Reactions
    Reactions in which two compounds react to form two new compounds, with no changes in oxidation number. Reactions in which the ions of two compounds exchange partners.

Method of Initial Rates
    Method of determining the rate-law expression by carrying out a reaction with different initial concentrations and analyzing the resultant changes in initial rates.

Miscibility
    The ability of one liquid to mix with (dissolve in) another liquid.

Mixture
    A sample of matter composed of two or more substances, each of which retains its identity and properties.

Moderator
    A substance such as hydrogen, deuterium, oxygen or paraffin capable of slowing fast nuetrons upon collision.

Molality
    Concentration expressed as number of moles of solute per kilogram of solvent.

Molarity
    Number of moles of solute per litre of solution.

Molar Solubility
    Number of moles of a solute that dissolve to produce a litre of saturated solution.

Molecular Equation
    Equation for a chemical reaction in which all formulas are written as if all substances existed as molecules; only complete formulas are used.

Molecular Formula
    Formula that indicates the actual number of atoms present in a molecule of a molecular substance.

Molecular Geometry
    The arrangement of atoms (not lone pairs of electrons) around a central atom of a molecule or polyatomic ion.

Molecular Orbital
    An orbit resulting from overlap and mixing of atomic orbitals on different atoms. An MO belongs to the molecule as a whole.

Molecular Orbital Theory
    A theory of chemical bonding based upon the postulated existence of molecular orbitals.

Molecular Weight
    The mass of one molecule of a nonionic substance in atomic mass units.

Molecule
    The smallest particle of an element or compound capable of a stable, independent existence.

Mole Fraction
    The number of moles of a component of a mixture divided by the total number of moles in the mixture.

Monoprotic Acid
    Acid that can form only one hydronium ion per molecule; may be strong or weak.
    Acid that contains one ionizable hydrogen atom per formula unit.

Mother Nuclide
    Nuclide that undergoes nuclear decay.

===============================================================================



Native State
    Refers to the occurrence of an element in an uncombined or free state in nature.

Natural Radioactivity
    Spontaneous decomposition of an atom.

Nernst Equation
    Corrects standard electrode potentials for nonstandard conditions.

Net Ionic Equation
    Equation that results from canceling spectator ions and eliminating brackets from a total ionic equation.

Neutralization
    The reaction of an acid with a base to form a salt and water. Usually, the reaction of hydrogen ions with hydrogen ions to form water molecules.

Neutron
    A neutral subatomic particle having a mass of 1.0087 amu.

Nickel-cadmium cell (Nicad battery)
    A dry cell in which the anode is Cd, the cathode is NiO2, and the electrolyte is basic.

Nitrogenases
    A class of enzymes found in bacteria within root nodules in some plants, which catalyze reactions by which N2 molecules from the air are converted to ammonia.
    For more information see Enzymes

Nitrogen Cycle
    The complex series of reactions by which nitrogen is slowly but continually recycled in the atmosphere, lithosphere and hydrosphere.

Noble Gases (Rare Gases)
    Elements of the periodic Group 0; also called rare gases; formerly called inert gases, He,Ne,Ar, Kr, Xe, Rn.

Nodal Plane
    A region in which the probability of finding an electron is zero.

Nonbonding Orbital
    A molecular orbital derived only from an atomic orbital of one atom; lends neither stability nor instability to a molecule or ion when populated with electrons.

Nonelectrolyte
    A substance whose aqueous solutions do not conduct electricity.

Nonpolar Bond
    Covalent bond in which electron density is symmetrically distributed

Nuclear Binding Energy
    Energy equivalent of the mass deficiency; energy released in the formation of an atom from the subatomic particles.

Nuclear Fission
    The process in which a heavy nucleus splits into nuclei of intermediate masses and one or more protons are emitted.

Nuclear Reaction
    Involves a change in the composition of a nucleus and can evolve or absorb an extraordinarily large amount of energy

Nuclear Reactor
    A system in which controlled nuclear fisson reactions generate heat energy on a large scale, which is subsequently converted into electrical energy.

Nucleons
    Particles comprising the nucleus; protons and neutrons.

Nucleus
    The very small, very dense, positively charged center of an atom containing protons and neutrons, as well as other subatomic particles.

Nuclides
    Refers to different atomic forms of all elements in contrast to ?isotopes?, which refer only to different atomic forms of a single element.

Nuclide Symbol
    Symbol for an atom A/Z E, in which E is the symbol of an element, Z is its atomic number, and A is its mass number.

===============================================================================


Octahedral
    A term used to describe molecules and polyatomic ions that have one atom in the center and six atoms at the corners of a octahedron.

Octane Number
    A number that indicates how smoothly a gasoline burns.

Octet Rule
    Many representative elements attain at least a share of eight electrons in their valence shells when they form molecular or ionic compounds; there are some limitations.

Oil
    Liquid triester of glycerol and unsaturated fatty acids.

Open Sextet
    Refers to species that have only six electrons in the highest energy level of the central element (many Lewis acids).

Optical Activity
    The rotation of plane polarized light by one of a pair of optical isomers.

Optical Isomers
    Stereoisomers that differ only by being nonsuperimposable mirror images of each other, like right and left hands, also called enantiomers.

Ore
    A natural deposit containing a mineral of an element to be extracted.

Organic Chemistry
    The chemistry of substances that contain carbon-hydrogen bonds.

Osmosis
    The process by which solvent molecules pass through a semipermable membrane from a dilute solution into a more concentrated solution.

Osmotic Pressure
    The hydrostatic pressure produced on the surface of a semipermable membrane by osmosis.

Ostwald Process
    A process for the industrial production of nitrogen oxide and nitric acid from ammonia and oxygen.

Outer Orbital Complex
    Valence bond designation for a complex in which the metal ion utilizes d orbitals in the outermost (occupied) shell in hybridization.

Overlap
    The interaction of orbitals on different atoms in the same region of space.

Oxidation
    An algebraic increase in the oxidation number; may correspond to a loss of electrons.

Oxidation Numbers
    Arbitrary numbers that can be used as mechanical aids in writing formulas and balancing equations; for single- atom ions they correspond to the charge on the ion; more electronegative atoms are assigned negative oxidation numbers (also called Oxidation states).

Oxidation-reduction Reactions
    Reactions in which oxidation and reduction occur; also called redox reactions.

Oxide
    A binary compound of oxygen.

Oxidizing Agent
    The substance that oxidizes another substance and is reduced.

================================================================================


Pairing
    A favourable interaction of two electrons wit    h opposite m , values in the same orbital.

Pairing Energy
    Energy required to pair two electrons in the same orbital.

Paramagnetism
    Attraction toward a magnetic field, stronger than diamagnetism, but still weak compared to ferromagnetism.

Partial Pressure
    The pressure exerted by one gas in a mixture of gases.

Particulate Matter
    Fine divided solid particles suspended in polluted air.

Pauli Exclusion Principle
    No two electrons in the same atom may have identical sets of four quantum numbers.

Percentage Ionization
    The percentage of the weak electrolyte that ionizes in a solution of given concentration.

Percent by Mass
    100% times the actual yield divided by theoretical yield.

Percent Composition
    The mass percent of each element in a compound.

Percent Purity
    The percent of a specified compound or element in an impure sample.

Period
    The elements in a horizontal row of the periodic table.

Periodicity
    Regular periodic variations of properties of elements with atomic number (and position in the periodic table).

Periodic Law
    The properties of the elements are periodic functions of their atomic numbers.

Periodic Table
    An arrangement of elements in order of increasing atomic numbers that also emphasizes periodicity.

Peroxide
    A compound containing oxygen in the -1 oxidation state. Metal peroxides contain the peroxide ion, O22-

pH
    Negative logarithm of the concentration (mol/L) of the H3O+[H+] ion; scale is commonly used over a range 0 to 14.

Phase Diagram
    Diagram that shows equilibrium temperature-pressure relationships for different phases of a substance.

Phenol
    Hydrocarbon derivative containing an [OH] group bound to an aromatic raing.

Photochemical Oxidants
    Photochemically produced oxidizing agents capable of causing damage to plants and animals.

Photochemical Smog
    A brownish smog occurring in urban areas receiving large amounts of sunlight; caused by photochemical (light-induced) reactions among nitrogen oxides, hydrocarbons and other components of polluted air that produce photochemical oxidants.

Photoelectric Effect
    Emission of an electron from the surface of a metal caused by impinging electromagnetic radiation of certain minimum energy; current increases with increasing intensity of radiation.

Photon
    A packet of light or electromagnetic radiation; also called quantum of light

Physical Change
    A change in which a substance changes from one physical state to another but no substances with different composition are formed. Example Gas to Liquid - Solid.

Plasma
    A physical state of matter which exists at extremely high temperatures in which all molecules are dissociated and most atoms are ionized.

Polar Bond
    Covalent bond in which there is an unsymmetrical distribution of electron density.

Polarimeter
    A device used to measure optical activity.

Polarization
    The buildup of a product of oxidation or a reduction of an electrode, preventing further reaction.

Polydentate
    Refers to ligands with more than one donor atom.

Polyene
    A compound that contains more than one double bond per molecule.

Polymerization
    The combination of many small molecules to form large molecules.

Polymer
    A large molecule consisting of chains or rings of linked monomer units, usually characterized by high melting and boiling points.

Polymorphous
    Refers to substances that crystallize in more than one crystalline arrangement.

Polyprotic Acid
    An Acid that can form two or more hydronium ions per molecule; often a least one step of ionization is weak.

Positron
    A Nuclear particle with the mass of an electron but opposite charge.

Potential Energy
    Energy that matter possesses by virtue of its position, condition or composition.

Precipitate
    An insoluble solid formed by mixing in solution the constituent ions of a slightly soluble solution.

Primary Standard
    A substance of a known high degree of purity that undergoes one invariable reaction with the other reactant of interest.

Primary Voltaic Cells
    Voltaic cells that cannot be recharged; no further chemical reaction is possible once the reactants are consumed.

Proton
    A subatomic particle having a mass of 1.0073 amu and a charge of +1, found in thew nuclei of atoms.

PseudobinaryIonic Compounds
    Compounds that contain more than two elements but are named like binary compounds.

========================================================================


Quantum Mechanics
    Mathematical method of treating particles on the basis of quantum theory, which assumes that energy (of small particles) is not infinitely divisible.

Quantum Numbers
    Numbers that describe the energies of electrons in atoms; derived from quantum mechanical treatment.

============================================================================



Radiation
    High energy particles or rays emitted during the nuclear decay processes.

Radical
    An atom or group of atoms that contains one or more unpaired electrons (usually very reactive species)

Radioactive Dating
    Method of dating ancient objects by determining the ratio of amounts of mother and daughter nuclides present in an object and relating the ratio to the object?s age via half-life calculations.

Radioactive Tracer
    A small amount of radioisotope replacing a nonradioactive isotope of the element in a compound whose path (for example, in the body) or whose decomposition products are to be monitored by detection of radioctivity; also called a radioactive label.

Radioactivity
    The spontaneous disintegration of atomic nuclei.

Raoult's Law
    The vapor pressure of a solvent in an ideal solution decreases as its mole fraction decreases.

Rate-determining Step
    The slowest step in a mechanism; the step that determines the overall rate of reaction.

Rate-law Expression
    Equation relating the rate of a reaction to the concentrations of the reactants and the specific rate of the constant.

Rate of Reaction
    Change in the concentration of a reactant or product per unit time.

Reactants
    Substances consumed in a chemical reaction.

Reaction Quotient
    The mass action expression under any set of conditions (not necessarily equlibrium); its magnitude relative to K determines the direction in which the reaction must occur to establish equilibrium.

Reaction Ratio
    The relative amounts of reactants and products involved in a reaction; maybe the ratio of moles. millimoles, or masses.

Reaction Stoichiometry
    Description of the quantitative relationships among substances as they participate in chemical reactions.

Reducing Agent
    The substance that reduces another substance and is oxidized.

Resonance
    The concept in which two or more equivalent dot formulas for the same arrangement of atoms (resonance structures) are necessary to describe the bonding in a molecule or ion.

Reverse Osmosis
    Forcing solvent molecules to flow through a semipermable membrane from a concentated solution into a dilute solution by the application of greater hydrostatic pressure on concentrated side than the osmotic pressure opposing it.

Reversible Reaction
    Reactions that do not go to completion and occur in both the forward and reverse direction.

================================================================================

Salt Bridge
    A U-shaped tube containing electrolyte, which connects two half-cells of a voltaic cell.

Saponification
    Hydrolysis of esters in the presence of strong soluable bases.

Saturated Hydrocarbons
    Hydrocarbons that contain only single bonds. They are also called alkanes or paraffin hydrocarbons.

Saturated Solution
    Solution in which no more solute will dissolve.

Second Law of Thermodynamics
    The universe tends toward a state of greater diorder in spontaneous processes.

Secondary Standard
    a solution that has been titrated against a primary standard. A standard solution is a secondary standard.

Secondary Voltaic Cells
    Voltaic cells that can be recharged; original reactanats can be regenerated be reversing the direction of the current flow.

Semiconductor
    A substance that does not conduct electricity at low temperatures but does so at higher temperatures.

Semipermable Membrane
    A thin partition between two solutions through which certain molecules can pass but others cannot.

Shielding Effect
    Electrons in filled sets of s , p orbitals between the nucleus and outer shell electrons shield the outer shell electrons somewhat from the effect of protons in the nucleus; also called screening effect.

Sigma Bonds
    Bonds resulting from the head-on overlap of atomic orbitals, in which the region of electron sharing is along and (cylindrically) symmetrical to the imaginary line connecting the bonded atoms.

Sigma Orbital
    Molecular orbital resulting from head-on overlap of two atomic orbitals.

Silicones
    Polymeric organosilicon compounds; contain individual or cross-linked Si-O chains or rings in which some oxygens of SiO4 tetrahedra are replaced by other groups.

Single Bond
    Covalent bond resulting from the sharing of two electrons (one pair) between two atoms.

Solubility Product Constant
    Equilibrium constant that applies to the dissolution of a slightly soluble compound.

Solubility Product Principle
    The solubility product constant expression for a slightly soluble compound is the product of the concentrations of the constituent ions, each raised to the power that corresponds to the number of ions in one formula unit.

Solute
    The dispersed (dissolved) phase of a solution.

Solution
    Homogeneous mixture of two or more substances.

Solvation
    The process by which solvent molecules surround and interact with solute ions or molecules.

Solvent
    The dispersing medium of a solution.

Solvolysis
    The reaction of a substance with the solvent in which it is dissolved.

S Orbital
    A spherically symmetrical atomic orbital; one per energy level.

Specific Gravity
    The ratio of the density of a substance to the density of water.

Specific Heat
    The amount of heat required to raise the temperature of one gram of substance one degree Celsius.

Specific Rate Constant
    An experimentally determined (proportionality) constant, which is different for different reactions and which changes only with temperature; k in the rate-law expression: Rate = k [A] x [B]v.

Spectator Ions
    Ions in a solution that do not participate in a chemical reaction.

Spectral Line
    Any of a number of lines corresponding to definite wavelengths of an atomic emission or absorption spectrum; represents the energy difference between two energy levels.

Spectrochemical Series
    Arrangement of ligands in order of increasing ligand field strength.

Spectrum
    Display of component wavelengths (colours) of electromagnetic radiation.

Square Planar
    A term used to describe molecules and polyatomic ions that have one atom in the center and four atoms at the corners of a square.

Square Planar Complex
    Complex in which the metal is in the center of a square plane, with ligand donor atoms at each of the four corners

Standard Electrodes
    Half-cells in which the oxidized and reduced forms of a species are present at unit activity; 1.0M solutions of dissolved ions, 1.0atm partial pressure of gases, and pure solids and liquids.

Standard Electrode Potential
    By convention , potential, Eo, of a half-reaction as a reduction relative to the standard hydrogen electrode when all species are present at unit activity.

Standard Entropy
    The absolute entropy of a substance in its standard state at 298 K.

Standard Molar Enthalphy of Formation
    The amount of heat absorbed in the formation of one mole of a substance in a specified state from its elements in their standard states.

Standard Molar Volume
    The volume occupied by one mole of an ideal gas under standard conditions; 22.4liters.

Standard Reaction
    A reaction in which the numbers of moles of reactants shown in the balanced equation, all in their standard states, are completely converted to the numbers of moles of products shown in the balanced equation, also sall at their standard state.

Stereoisomers
    Isomers that differ only in the way that atoms are oriented in space; consist of geometrical and optical isomers.

Stoichiometry
    Description of the quantitative relationships among elements and compounds as they undergo chemical changes.

Strong Electrolyte
    A substance that conducts electricity well in a dilute aqueous solution.

Strong Field Ligand
    Ligand that exerts a strong crystal or ligand electrical field and generally forms low spin complexes with metal ions when possible.

Structural Isomers
    Compounds that contain the same number of the same kinds of atoms in different geometric arrangements.

Sublimation
    The direct vaporization of a sold by heating without passing through the liquid state.

Substance
    Any kind of matter all specimens of which have the same chemical composition and physical properties.

Substitution Reaction
    A reaction in which an atom or a group of atoms is replaced by another atom or group of atoms.

Supercooled Liquids
    Liquids that, when cooled, apparently solidify but actually continue to flow very slowly under the influence of gravity.

Supercritical Fluid
    A substance at temperature above its critical temperature.

Supersaturated Solution
    A solution that contains a higher than saturation concentration of solute; slight disturbance or seeding causes crystallization of excess solute.

Suspension
    A heterogeneous mixture in which solute-like particles settle out of solvent-like phase some time after their introduction.
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Temperature
    A measure of the intensity of heat, i.e. the hotness or coldness of a sample. or object.

Ternary Acid
    A ternary compound containing H, O, and another element, often a nonmetal.

Ternary Compound
    A compound consisting of three elements; may be ionic or covalent.

Tetrahedral
    A term used to describe molecules and polyatomic ions that have one atom in center and four atoms at the corners of a tetrahedron.

Theoretical Yield
    Maximum amount of a specified product that could be obtained from specified amounts of reactants, assuming complete consumption of limiting reactant according to only one reaction and complete recovery of product. (Compare with Actual Yield)

Thermal Cracking
    Decomposition by heating a substance in the presence of a catalyst and in the absence of air.

Thermodynamics
    The study of the energy transfers accompanying physical and chemical processes.

Thermonuclear Energy
    Energy from nuclear fusion reactions.

Third Law of Thermodynamics
    The entropy of a hypothetical pure, perfect, crystalline sustance at absolute zero temperature is zero.

Titration
    A Procedure in which one solution is added to another solution until the chemical reaction between the two solutes is complete; the concentration of one solution is known and that of the other is unknown.

Total Ionic Equation
    Equation for a chemical reaction written to show the predominant form of all species in aqueous solution or in contact with water.

Transition State Theory
    Theory of reaction rates that states that reactants pass through high-energy transition states before forming products.

Tyndall Effect
    The scattering of light by colloidal particles.
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Unsaturated Hydrocarbons
    Hydrocarbons that contain double or triple carbon-carbon bonds.
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Valence Bond Theory
    Assumes that covalent bonds are formed when atomic orbitals on different atoms overlap and the electrons are shared.

Valence Electrons
    Outermost electrons of atoms; usually those involved in bonding.

Valence Shell Electron Pair Repulsion Theory
    Assumes that electron pairs are arranged around the central element of a molecule or polyatomic ion so that there is maximum separation (and minimum repulsion) among regions of high electron density.

van der Waals' Equation
    An equation of state that extends the ideal gas law to real gases by inclusion of two empirically determined parameters, which are different for different gases.

Vapor
    A gas formed by boiling or evaporating a liquid.

Vapor Pressure
    The particle pressure of a vapor at the surface of its parent liquid.

Voltage
    Potential difference between two electrodes; a measure of the chemical potential for a redox reaction to occur.

Voltaic Cells
    Electrochemical cells in which spontaneous chemical reactions produce electricity; also called galvanic cells.
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Water Equivalent
    The amount of water that would absorb the same amount of heat as the calorimeter per degree temperature increase.

Weak Electrolyte
    A substance that conducts electricity poorly in a dilute aqueous solution.

Weak Field Ligand
    A Ligand that exerts a weak crystal or ligand field and ge- nerally forms high spin complexes with metals.
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Zone Refining
    A method of purifying a bar of metal by

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