Chemistry GCSE Dictionary

AcidA chemical that produces hydrogen ions when it dissolves in water.
Activation energyThe minimum amount of energy required for a given chemical reaction to take place.
AlkaliA base that is soluble in water.
AlloyA metallic substance madeby comtwo or more metals.
AnhydrousAn anhydrous substance does not contain any water.
AnodeElectrode where oxidation occurs.
Atomic numberThe number of protons in a nucleus, symbol Z (also known as the proton number).
BasesChemicals which react with acids to neutralise them.
Bond energyThe energy required to break a particular chemical bond.
CatalystA substance that incthe rate of another reaction but is not used up or changed itself.
CathodeElectrode where reduction occurs
ChromatographyA technique for separatia mixture of substances using a stationary and a moving phase.
Collision theoryAn explanation of chemical reactions in terms of thereactant particlescolliding with sufficient energy for a reaction to take place.
Covalent bondThe chemical bond made when atoms join together by sharing electrons.
DissociationThe separation of a chetwo or more simpler substances, or of a molecule into atoms or ions.
ElectrolyteA substance that conducts electricity when molten or in aqueous sol.
ElectrolysisUsing eleto drive a redox reaction.
Electronic structureThe arrangement of electrons in an atom.
Empirical formulaA chemical formula showing the ratio of the number of atoms in a compound.
EndothermicA reaction that involves a net absorption of energy.
EquilibriumThe point at which a reversible reaction happens at exactly the same rate in both directions.
ExothermicA reaction that involves a net release of energy.
Fractional distillationA way of separating a mixture of substances by their different boiling points.
Giant covalent structuresGiant structures held together by many covalent bonds which give them high melting points and hardness, e.g. diamond and quartz.
HydratedA hydrated subwater.
HydrocarbonA compound made of only carbon and hydrogen.
IndicatorA chemical that changes colour according to the pH of the solution it is in.
Intermolecular forcesForces of attraction between molecules.
Ionic bondA chemical bond made when one atom gives up one or more electrons to another atom.
IonisationAny process in which atoms become charged by gaining or losing electrons.
IsotopesAtoms of the same element which have different numbers of neutrons.
Mass numberThe total number of protons and neutrons in an atom (symbol A).
Mass spectrometerAn instrument used to measure the masses of atoms and molecules.
MoleA unit of measurement for the amount of substance, equ6.×1023particles.
Molecular formulaA formula that shows the numbers of the different kinds of atoms in a molecule.
OxidationThe loss of electrons.
Ozone layerThe layer of ozone gas in the Earth’s atmosphere that absorbs ultraviolet radiation.
Percentage yieldThe percentage of product formed in a chemical reaction as a perofthe maximum possible amount of product that could be formed.
PolymerA substance consisting of very large molecules made of smaller molecules called monomers.
Proton acceptorThe modern definition of an alkali.
Proton donorThe modern definition of an acid.
RedoxA reaction where electrons are lost by one substance and gained by another.
ReductionThe gain of electrons.
Relative atomic massThe mass of an atom compared with an atom of 12.
Reversible reactionA reaction in which the products react together to produce the original reactants.
ShellsThe region where eleare locatedas they travel around the nucleus of an atom.
SolubilityThe extent to which a solute will dissolve in a sol.
Thermal decompositionThe splitting up of a substance by heat.
TitrationA commethod for measuring the amount of substance in a solution.
Transition metalsThe block of metallic elements in the middle of the periodic table.
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