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Category: Sciences > Chemical
Date & country: 10/12/2007, UK
Words: 611

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.

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

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.

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.

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.

Nitric Acid
HNO3: Transparent colorless or yellowish, fuming, suffocating, caustic and corrosive liquid, boiling point 83C. A 70 percent solution is used in the S.S.E. laboratory for junction depth measurements. Nitric acid is also present in the metal etch solution used for the Aluminum etch procedure.

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

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.

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.

A substance whose aqueous solutions do not conduct electricity.

Nonpolar Bond
Covalent bond in which electron density is symmetrically distributed

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.

Particles comprising the nucleus, protons and neutrons.

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

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.

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

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.

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

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

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.

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

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.

A binary compound of oxygen.

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

A favourable interaction of two electrons with opposite m , values in the same orbital.

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

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.

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.

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

The elements in a horizontal row of 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.

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

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

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.

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

Phosphoric Acid
H3P04, Colorless liquid or rhombic crystals, decomposes before it will boil. Used mostly in the metal etchant.

Phosphorus Oxychloride
Colorless to slightly yellow fuming liquid.Mol. Wt.: 153.39M.P.: 20CB.P.: 105.1CDensity: 1.685 @ 15.5CVapor Pressure: 40 mm @ 27.3CVapor Density: 5.3Used as the phosphorus source for phosphorus diffusion.

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.

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.

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.

A device used to measure optical activity.

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

Refers to ligands with more than one donor atom.

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

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

The combination of many small molecules to form large molecules.

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.

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.

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.

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.

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

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.

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

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