AQA A Level Chemistry Definitions
Relative Atomic Mass - answerThe weighted mean mass of an atom of an element relative to
1/12 of the mass of one atom of carbon-12
First Ionisation energy - answerThe energy required to remove an electron from each atom in
one mole of gaseous atoms
Acid - answ...
Relative Atomic Mass - answer✔✔The weighted mean mass of an atom of an element relative to
1/12 of the mass of one atom of carbon-12
First Ionisation energy - answer✔✔The energy required to remove an electron from each atom in
one mole of gaseous atoms
Acid - answer✔✔A species that is a proton donor
Activation Energy - answer✔✔The minimum energy required to start a reaction by the breaking
of bonds
Addition Polymer - answer✔✔The process in which unsaturated alkene molecules ass on to a
growing polymer chain one at a time to form a very long saturated molecule chain
Addition Reaction - answer✔✔A reaction in which a reactant is added to an unsaturated
molecule to make a saturated molecule
Adsorption - answer✔✔The process that occurs when a gas, liquid or solid is held to the surface
of a solid, or, more rarely, a liquid
Alicyclic Hydrocarbon - answer✔✔A hydrocarbon with carbon atoms joined together in a ring
structure
Aliphatic Hydrocarbon - answer✔✔A hydrocarbon with carbon atoms joined together in straight
or branched chains
Alkali - answer✔✔A type of base that dissolves in water forming hydroxide ions
Alkanes - answer✔✔The homologous series with the general formula CnH2n+2
Alkyl Group - answer✔✔An alkane with a hydrogen ion removed. Alkyl groups are often shown
as 'R'
Amount of Substance - answer✔✔The quantity whose unit is the mole
Anhydrous - answer✔✔A substance containing no water molecules
Atom Economy - answer✔✔(molecular mass of the desired product/sum of molecular masses of
all products) x100
Atomic Orbital - answer✔✔A region within an atom that can hold up to two electrons, with
opposite spins
Atomic Number - answer✔✔The number of protons in the nucleus of an atom
Average Bond Enthalpy - answer✔✔The average enthalpy change that takes place when
breaking by homolytic fission 1 mol of a given type of bond in the molecules of a gaseous
substance
Avogadro Constant - answer✔✔The number of atoms per mole of the carbon-12 isotope. (6.02 x
10^23)
Base - answer✔✔A species that is a proton acceptor
Biodegradable Material - answer✔✔A substance that is broken down naturally in the
environment of a living organism
Boltzmann Distribution - answer✔✔The distribution of energies of molecules at a particular
temperature, usually shown as a graph.
Bond Enthalpy - answer✔✔The enthalpy change hat takes place when breaking by homolytic
fission 1 mol of a given bond in the molecules of a gaseous species
Carbanion - answer✔✔An organic ion in which a carbon atom has a negative charge
Carbocation - answer✔✔An organic ion in which a carbon ion has a positive charge.
Catalyst - answer✔✔A substance that increases the rate of a chemical reaction without it being
used up
Cation - answer✔✔A positively charged ion
Cis-Trans Isomerism - answer✔✔A special type of E/Z isomerism in which there is a non-
hydrogen group and a hydrogen on each C of a C=C double bond: the cis isomer has the H atom
of each carbon on the same side, the trans isomer has the H atom of each carbon on different
sides
Compound - answer✔✔A substance formed from two or more chemically bonded elements in a
fixed ratio, usually shown by a chemical formula.
Concentration - answer✔✔The amount of solute, in mol, per 1 dm^2
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