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

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.

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.

Helium
Discovered : by Sir William Ramsay in London, and independently by P.T. Cleve and N.A. Langlet in Uppsala, Sweden in 1895Origin : The name is derived from the Greek ‘helios`,sunDescription :A colourless, odourless gas that is totally unreactive. It is extracted from natural gas wells, some of which contain gas that is 7% helium. It is used in deep …

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.

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.The process is called Homogeneous 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.

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
Discovered : by Henry Cavendish in 1766Isolated in London, UKOrigin : The name is derived from the Greek ‘hydro genes`, meaning water forming.Description :A colourless, odourless gas that burns and can form an explosive mixture with air. It is currently manufactured from methane gas, but is also produced by the electrolysis of water and aqueous sal…

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.

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

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

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.

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.

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

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.

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

Inhibitory Catalyst
An inhibitor, a catalyst that decreases the rate of reaction.

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.

Insoluble Compound
A very slightly soluble compound.

Insulator
Poor electric and heat conductor.

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.

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

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

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

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.

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

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

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

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

Ioniztion
The breaking up of a compound into separate ions.

Iron
Discovered : known to ancient civilisationsOrigin : The name comes from the Anglo-Saxon ‘iren`, and the symbol from the Latin ‘ferrum`, meaning iron.Description :Iron is an enigma - it rusts easily and yet is the most important of all metals, world production exceeds 700 million tons a year. Small amounts of carbon are added to iron to produce stee…

Isoelectric
Having the same electronic configurations.

Isomers
Different substances that have the same formula

Isomorphous
Refers to crystals having the same atomic arrangement.

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.

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.

Lanthanides
Elements 58 to 71 (after lanthanum)

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.

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.

Lead Storage Battery
Secondary voltaic cell used in most automobiles.

Leclanche Cell
A common type of dry cell.

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.

Ligand
A Lewis base in a coordination compound.

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

Line Spectrum
An atomic emission or absorption spectrum.

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

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.

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.