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AllChemicals.info - Chemical glossary Category: Sciences > Chemical Date & country: 10/12/2007, UK Words: 611

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.

Dubnium
Discovered : at both Berkeley, California, USA, and Dubna, near Moscow, Russia in 1970Description:A highly radioactive metal which does not occur naturally, and of which only a few atoms have ever been made. It is of research interest only.Origin:The element is named after the Russian town of Dubna.

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.

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.

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

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

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

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.

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

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.

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

Endothermic
Describes processes that absorb heat energy.

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

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.

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 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.

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.

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.

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.

Evaporization
Vaporization of a liquid below its boiling point.

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.

Faraday
One faraday of electricity corresponds to the charge on 6.022 x 10²³ electrons, or 96,487.301 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.

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.

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.

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.

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

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.

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

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.

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.

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 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 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.

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

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.

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.