OCR AS Chemistry glossary - ALL DEFINITIONS (unit 1 and 2)

OCR AS Chemistry glossary - ALL DEFINITIONS (unit 1 and 2)

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acid A species that is a proton donor.
activation energy The minimum energy required to start a reaction by the breaking
of bonds.
addition polymer A very long molecular chain formed by repeated addition reactions
of many unsaturated alkene molecules (monomers).
addition The process in which unsaturated alkene molecules (monomers)
polymerisation add on to a growing polymer chain one at a time to form a very
long saturated molecular chain (the addition polymer).
addition reaction A reaction in which a reactant is added to an unsaturated
molecule to make a saturated molecule.
adsorption The process that occurs when a gas, liquid or solute is held to the
surface of a solid or, more rarely, a liquid.
alicyclic hydrocarbon A hydrocarbon with carbon atoms joined together in a ring
aliphatic hydrocarbon A hydrocarbon with carbon atoms joined together in straight or
branched chains.
alkali A type of base that dissolves in water forming hydroxide ions,
OH­(aq) ions.
alkanes The homologous series with the general formula: CnH2n+2.
alkyl group An alkane with a hydrogen atom removed, e.g. CH3, C2H5 alkyl
groups are often shown as `R'.
amount of substance The quantity whose unit of the mole. Chemists use `amount of
substance' as a means of counting atoms.
anhydrous A substance that contains no water molecules.
anion A negatively charged ion.
atom economy
atomic orbital A region within an atom that can hold up to two electrons, with
opposite spins.
atomic (proton) The number of protons in the nucleus of an atom.

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The average enthalpy change that takes place when breaking by
enthalpy homolytic fission 1 mol of a given type of bond in the molecules of
a gaseous species.
Avogadro constant, NA The number of atoms per mole of the carbon12 isotope
(6.02 × 1023 mol­1).
base A species that is a proton acceptor.
biodegradable material A substance that is broken down naturally in the environment by
living organisms.
Boltzmann distribution The distribution of energies of molecules at a particular
temperature, usually shown as a graph.…read more

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A shared pair of electrons which has been provided by one of the
bonding atoms only also called a coordinate bond.
dehydration An elimination reaction in which water is removed from a
saturated molecule to make an unsaturated molecule.
delocalised electrons Electrons that are shared between more than two atoms.
displacement reaction A reaction in which a more reactive element displaces a less
reactive element from an aqueous solution of the latter's ions.…read more

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H The heat content that is stored in a chemical system.
(standard) enthalpy The enthalpy change that takes place when one mole of a
change of substance reacts completely with oxygen under standard
combustion, Hc conditions, all reactants and products being in their standard
(standard) enthalpy The enthalpy change that takes place when one mole of a
change of formation, compound is formed from its constituent elements in their
Hf standard states under standard conditions.…read more

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A threedimensional structure of positive ions and delocalised
electrons, bonded together by strong metallic bonds.
greenhouse effect The process in which the absorption and subsequent emission of
infrared radiation by atmospheric gases warms the lower
atmosphere and the planet's surface.
group A vertical column in the Periodic Table. Elements in a group have
similar chemical properties and their atoms have the same
number of outer shell electrons.…read more

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­dipole forces), permanent dipole­dipole forces or
hydrogen bonds.
ion A positively or negatively charge atom or (covalently bonded)
group of atoms (a molecular ion).
ionic bonding The electrostatic attraction between oppositely charged ions.
(first) ionisation The energy required to remove one electron from each ion in one
energy mole of gaseous atoms to form one mole of gaseous 1+ ions.…read more

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M+ The positive ion formed in mass spectrometry when a molecule
loses an electron.
molecule A small group of atoms held together by covalent bonds.
monomer A small molecule that combines with many other monomers to
form a polymer.
nomenclature A system of naming compounds.
nucleophile An atom (or group of atoms) that is attracted to an
electrondeficient centre or atom, where it donates a pair of
electrons to form a new covalent bond.…read more

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The formation of a solid from a solution during a chemical
reaction. Precipitates are often formed when two aqueous
solutions are mixed together.
principal quantum A number representing the relative overall energy of each orbital,
number, n which increases with distance from the nucleus. The sets of
orbitals with the same n value are referred to as electron shells or
energy levels.
propagation The two repeated steps in radical substitution that build up the
products in a chain reaction.…read more

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A group of atomic orbitals with the same principal quantum
number, n. Also known as a main energy level.
simple molecular A threedimensional structure of molecules, bonded together by
lattice weak intermolecular forces.
skeletal formula A simplified organic formula, with hydrogen atoms removed from
alkyl chains, leaving just a carbon skeleton and associated
functional groups.
species Any type of particle that takes part in a chemical reaction.…read more

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The step at the end of a radical substitution when two radicals
combine to form a molecule.
thermal The breaking up of a chemical substance with heat into at least
decomposition two chemical substances.
troposphere The lowest layer of the Earth's atmosphere, extending from the
Earth's surface up to about 7 km (above the poles) and to about
20 km (above the tropics).
unsaturated A hydrocarbon containing carbontocarbon multiple bonds.
van der Waals' forces Very weak attractive forces between induced dipoles in
neighbouring molecules.…read more


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