Copy of `AllChemicals.info - Chemical glossary`
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AllChemicals.info - Chemical glossary
Category: Sciences > Chemical
Date & country: 10/12/2007, UK Words: 611
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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 ZeroThe zero point on the absolute temperature scale, -273.15°C or 0 K, theoretically, the temperature at which molecular motion ceases. The concept of an absolute zero temperature was first deduced from experiments with gases. When a fixed volume of gas is cooled, its pressure decreases with its temperature.Absolute zero can't be reached through exper…
Absorption SpectrumSpectrum associated with absorption of electromagnetic radiation by atoms (or other species) resulting from transitions from lower to higher energy states. An absorption spectrum is the inverse of an emission spectrum.
AccuracyHow closely a measured value agrees with the correct value.
Acetic AcidCA
3COOH, clear, colorless liquid, pungent odor. Boiling point 140C, flash point 54C (closed cup), autoignition temperature 38OC. A 99.7% solution is used in the S.S.E. laboratory for junction depth measurements. Acetic acid is also present in the metal etch solution used for Aluminum etch procedure.
AcidA 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. Acids taste sour, turn litmus red, gives a solution with a pH of less than 7 when dissolved in water and often react with some metals to produce hydrogen gas.
Acid AnhydrideCompound produced by dehydration of a carbonic acid. General formula is R--C--O--C--R. Chemical compound that reacts with water to form an acid and are usually oxides of nonmetallic elements. Anhydrides are generally more reactive than their corresponding acids because they are able to react with water to form their corresponding acid.
Acidic SaltA salt containing an ionizable hydrogen atom, does not necessarily produce acidic solutions.
ActinidesElements 89 to 103 (between lawrencium and actinium) on the periodic table. Only the first four have been found in nature in appreciable amounts. The remainder have been produced synthetically.
Activation EnergyAmount of energy that must be absorbed by reactants in their ground states to reach the transition state so that a reaction can occur. In other words, activation energy is the minimum energy required for a chemical reaction to occur.
Active MetalMetal with low ionization energy that loses electrons readily to form cations.
Activity SeriesA listing of metals (and hydrogen) in order of decreasing activity.
Actual YieldAmount of a specified pure product actually obtained from a given reaction. Compare with Theoretical Yield.
Acyl GroupCompound derived from a carbonic acid by replacing the --OH group with a halogen (X), usually --Cl, general formula is O R--C--X.
Addition ReactionA reaction in which two atoms or groups of atoms are added to a molecule, one on each side of a double or triple bond. Types of addition reaction include electrophilic, nucleophilic (polar) and free radical addition (non-polar).
Adhesive ForcesForces of attraction between a liquid and another surface.
AdsorptionAdhesion of a species onto the surfaces of particles
AlcoholHydrocarbon derivative containing an --OH group attached to a carbon atom not in an aromatic ring. Alcohols are a class of organic compounds containing the hydroxyl group, OH, attached to a carbon atom.Alcohols are neither acid nor alkaline. They are characterized by many common reactions, the most important of which is the reaction with acids form…
AldehydeCompound 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 MetalsMetals of Group IA (Na, K, Rb).
Alkaline BatteryA dry cell in which the electrolyte contains KOH.
Alkaline Earth MetalsGroup IIA metals
Alkenes (Olefins)Unsaturated hydrocarbons that contain one or more carbon-carbon double bonds.
Alkyl GroupA group of atoms derived from an alkane by the removal of one hydrogen atom.
AlkylbenzeneA compound containing an alkyl group bonded to a benzene ring.
AlkynesUnsaturated hydrocarbons that contain one or more carbon-carbon triple bonds.
AllotropesDifferent forms of the same element in the same physical state.
AlloyingMixing of metal with other substances (usually other metals) to modify its properties.
Alpha (a) ParticleHelium ion with 2
+ charge, an assembly of two protons and two neutrons.
Alpha ParticlesA helium nucleus.
AlumsHydrated sulfates of the general formula M+M3+(SO4)2.12H2).
AmideCompound 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.
AmineDerivatives of ammonia in which one or more hydrogen atoms have been replaced by organic groups.
Amine ComplexesComplex species that contain ammonia molecules bonded to metal ions.
Amino AcidCompound containing both an amino and a carboxylic acid group.The --NH2 group.
Amorphous SolidA noncrystalline solid with no well-defined ordered structure.
AmpereUnit of electrical current, one ampere equals one coulomb per second.
AmphiprotismAbility of a substance to exhibit amphiprotism by accepting donated protons.
AmphoterismThe ability to react with both acids and bases.Ability of substance to act as either an acid or a base.
AnionA negative ion, an atom or goup of atoms that has gained one or more electrons.
AnodeIn a cathode ray tube, the positive electrode. Electrode at which oxidation occurs.
Antibonding OrbitalA 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 HydrocarbonsBenzene and its derivatives.
Artificial TransmutationAn artificially induced nuclear reaction caused by the bombardment of a nucleus with subatomic particiles or small nucei.
Aryl GroupGroup of atoms remaining after a hydrogen atom is removed from the aromatic system.
Associated IonsShort-lived species formed by the collision of dissolved ions of opposite charges.
AtmosphereA unit of pressure, the pressure that will support a column of mercury 760 mm high at 0 °C.
AtomThe 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 NumberIntegral number of protons in the nucleus, defines the identity of element.
Atomic OrbitalRegion or volume in space in which the probability of finding electrons is highest.
Atomic RadiusRadius of an atom.
Atomic WeightWeighted average of the masses of the constituent isotopes of an element, The relative masses of atoms of different elements.
Aufbau ('building up') PrincipleDescribes the order in which electrons fill orbitals in atoms.
AutoionizationAn ionization reaction between identical molecules.
Avogadro's LawAt the same temperature and pressure, equal volumes of all gases contain the same number of molecules.
Avogadro's NumberThe number (6.022x10^23) of atoms, molecules or particles found in exactly 1 mole of substance.
Background RadiationRatiation extraneous to an experiment. Usually the low-level natural radiation form cosmic rays and trace radioactive substances present in our environment.
BandA series of very closely spaced, nearly continuous molecular orbitals that belong to the crystal as a whole.
Band of StabilityBand containing nonradioactive nuclides in a plot of number of neutrons versus atomic number.
Band Theory of MetalsTheory that accounts for the bonding and properties of metallic solids.
BarometerA device for measuring pressure.
BaseA 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 AnhydrideThe oxide of a metal that reacts with water to form a base.
Basic SaltA salt containing an ionizable OH group.
Beta ParticleElectron emitted from the nucleus when a neuton decays to a proton and an electron.
Binary AcidA binary compound in which H is bonded to one or more of the more electronegative nonmetals.
Binary CompoundA compound consisting of two elements, may be ionic or covalent.
BiodegradabilityThe ability of a substance to be broken down into simpler substances by bacteria.
Boiling PointThe temperature at which the vapor pressure of a liquid is equal to the applied pressure, also the condensation point
Boiling Point ElevationThe increase in the boiling point of a solvent caused by the dissolution of a nonvolatile solute.
Bomb CalorimeterA device used to measure the heat transfer between system and surroundings at constant volume.
Bond EnergyThe 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 OrderHalf the numbers of electrons in bonding orbitals minus half the number of electrons in antibonding orbitals.
Bonding OrbitalA 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 PairPair of electrons involved in a covalent bond.
Born-Haber CycleA 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.)
Boron HydridesBinary compounds of boron and hydrogen.
Boyle's LawAt constant temperature the volume occupied by a definite mass of a gas is inversely proportional to the applied pressure.
Breeder ReactorA nuclear reactor that produces more fissionable nuclear fuel than it consumes.
Bronsted-Lowry AcidA proton donor.
Bronsted-Lowry BaseA proton acceptor
Buffer SolutionSolution 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.
BuretA 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.
CalorieThe 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.
CalorimeterA device used to measure the heat transfer between system and surroundings.
Canal RayStream of positively charged particles (cations) that moves toward the negative electrode in cathode ray tubes, observed to pass through canals in the negative electrode.
CapillaryA tube having a very small inside diameter.
Capillary ActionThe 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.
CarbanionAn organic ion carrying a negative charge on a carbon atom.
Carbonium ionAn orgainic ion carrying a positive charge on a carbon atom.
CarcinogenA substance capable of causing or producing cancer in mammals.
CatalystA 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.
CatenationBonding 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.
CathodeElectrode at which reduction occurs in a cathode ray tube, the negative electrode.
Cathode Ray TubeClosed 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.
Cathodic ProtectionProtection of a metal (making ir a cathode) against corrosion by attaching it to a sacrifical anode of a more easily oxidized metal.
CationA positive ion, an atom or group of atoms that has lost one or more electrons.
Cell PotentialPotential difference, Ecell, between oxidation and reduction half-cells under nonstandard conditions.
Central AtomAn atom in a molecule or polyatomic ion that is bonded to more than one other atom.