| Acid | A chemical that produces hydrogen ions when it dissolves in water. |
| Activation energy | The minimum amount of energy required for a given chemical reaction to take place. |
| Alkali | A base that is soluble in water. |
| Alloy | A metallic substance madeby comtwo or more metals. |
| Anhydrous | An anhydrous substance does not contain any water. |
| Anode | Electrode where oxidation occurs. |
| Atomic number | The number of protons in a nucleus, symbol Z (also known as the proton number). |
| Bases | Chemicals which react with acids to neutralise them. |
| Bond energy | The energy required to break a particular chemical bond. |
| Catalyst | A substance that incthe rate of another reaction but is not used up or changed itself. |
| Cathode | Electrode where reduction occurs |
| Chromatography | A technique for separatia mixture of substances using a stationary and a moving phase. |
| Collision theory | An explanation of chemical reactions in terms of thereactant particlescolliding with sufficient energy for a reaction to take place. |
| Covalent bond | The chemical bond made when atoms join together by sharing electrons. |
| Dissociation | The separation of a chetwo or more simpler substances, or of a molecule into atoms or ions. |
| Electrolyte | A substance that conducts electricity when molten or in aqueous sol. |
| Electrolysis | Using eleto drive a redox reaction. |
| Electronic structure | The arrangement of electrons in an atom. |
| Empirical formula | A chemical formula showing the ratio of the number of atoms in a compound. |
| Endothermic | A reaction that involves a net absorption of energy. |
| Equilibrium | The point at which a reversible reaction happens at exactly the same rate in both directions. |
| Exothermic | A reaction that involves a net release of energy. |
| Fractional distillation | A way of separating a mixture of substances by their different boiling points. |
| Giant covalent structures | Giant structures held together by many covalent bonds which give them high melting points and hardness, e.g. diamond and quartz. |
| Hydrated | A hydrated subwater. |
| Hydrocarbon | A compound made of only carbon and hydrogen. |
| Indicator | A chemical that changes colour according to the pH of the solution it is in. |
| Intermolecular forces | Forces of attraction between molecules. |
| Ionic bond | A chemical bond made when one atom gives up one or more electrons to another atom. |
| Ionisation | Any process in which atoms become charged by gaining or losing electrons. |
| Isotopes | Atoms of the same element which have different numbers of neutrons. |
| Mass number | The total number of protons and neutrons in an atom (symbol A). |
| Mass spectrometer | An instrument used to measure the masses of atoms and molecules. |
| Mole | A unit of measurement for the amount of substance, equ6.×1023particles. |
| Molecular formula | A formula that shows the numbers of the different kinds of atoms in a molecule. |
| Oxidation | The loss of electrons. |
| Ozone layer | The layer of ozone gas in the Earth’s atmosphere that absorbs ultraviolet radiation. |
| Percentage yield | The percentage of product formed in a chemical reaction as a perofthe maximum possible amount of product that could be formed. |
| Polymer | A substance consisting of very large molecules made of smaller molecules called monomers. |
| Proton acceptor | The modern definition of an alkali. |
| Proton donor | The modern definition of an acid. |
| Redox | A reaction where electrons are lost by one substance and gained by another. |
| Reduction | The gain of electrons. |
| Relative atomic mass | The mass of an atom compared with an atom of 12. |
| Reversible reaction | A reaction in which the products react together to produce the original reactants. |
| Shells | The region where eleare locatedas they travel around the nucleus of an atom. |
| Solubility | The extent to which a solute will dissolve in a sol. |
| Thermal decomposition | The splitting up of a substance by heat. |
| Titration | A commethod for measuring the amount of substance in a solution. |
| Transition metals | The block of metallic elements in the middle of the periodic table. |
