| A | B |
|---|
| acid | A species that can donate a hydrogen ion (a proton donor). |
| activation energy, Ea | The minimum energy required for a collision between particles to result in a reaction. |
| addition reaction | A reaction in which a molecule is added across a double bond, resulting in a saturated product. |
| aliphatic | An organic molecule in which the carbon atoms are arranged in a straight or branched chain. |
| alkali | A soluble base. |
| amphoteric | Describes a compound that can react as an acid and a base. |
| aromatic | Describes an organic molecule that contains at least one benzene ring. |
| atomic number | The number of protons in the nucleus of an atom. |
| base | A species that can accept a hydrogen ion (a proton acceptor). |
| batch process | A process in which the products are removed at the end of the reaction. The reaction is then started again with a new supply of reactants. |
| bond angle | The angle formed between two bonds attached to the same atom. |
| bond dissociation energy | The energy needed to break a particular covalent bond. |
| calorimeter | The apparatus in which heat energy changes are measured. |
| carbocation | A very reactive species with a positive charge on a carbon atom. |
| carbonium ion | An alternative name for a carbocation. |
| catalyst | A substance that alters the rate of a chemical reaction, without itself being changed by the reaction. |
| chain isomers | Isomers in which the carbon atoms in the chain are arranged in a different pattern. |
| compound | A substance made up of more than one sort of atom bonded together. |
| continuous process | A reaction in which more reactants are added as the products are removed. |
| co-ordinate bond | A covalent bond in which both members of the pair of electrons are provided by one of the atoms. Also called a dative bond. |
| covalent bond | A bond formed by the sharing of a pair of electrons. |
| cracking | A process by which large molecules are broken down into smaller molecules. |
| dative bond | An alternative name for a co-ordinate bond. |
| dehydration | A reaction that involves the loss of a water molecule. |
| delocalised electrons | Electrons that are free to move and are not confined to a particular atom or bond. |
| diatomic molecule | A molecule containing two atoms. |
| electronegativity | A measure of the ability of an atom to attract the pair of electrons in a covalent bond. |
| electronic structure | The arrangement of the electrons in the energy levels of an atom or ion. |
| electrophile | An electron-deficient species that can accept a lone pair of electrons. |
| element | A substance made up of one sort of atom. |
| elimination reaction | A reaction in which a double bond is formed as a small molecule is lost from a saturated compound. |
| empirical formula | The simplest whole-number ratio of the atoms present in a molecule. |
| endothermic reaction | A reaction that absorbs heat energy (from the surroundings). |
| enthalpy change, ?H | The heat energy change in a reaction occurring at constant pressure. |
| equilibrium | A reaction in which the rates of the forward and reverse reactions are equal. |
| exothermic reaction | A reaction that releases heat energy (to the surroundings). |
| fractional distillation | A process that separates the hydrocarbons present in petroleum according to their boiling points. |
| free radical | A very reactive species with an unpaired electron. |
| functional group | The atom or group of atoms responsible for the chemical properties of an organic molecule. |
| geometrical isomers | Isomers in which the presence of a double bond results in the different orientation of some atoms or groups of atoms within the molecules. |
| halogen | Any element from Group 7 of the Periodic Table. |
| Hesss Law | The enthalpy change in a reaction is independent of the route of the reaction. |
| homologous series | A group of compounds that have the same functional group and similar chemical properties and that show a gradation in physical properties. |
| hydrocarbon | A compound containing the elements carbon and hydrogen only. |
| hydrogenation | A reaction in which hydrogen is added to a compound. |
| hydrolysis | A reaction with water. |
| intermediate | A species that is formed and used up during a reaction. |
| intermolecular forces | The weak forces of attraction between molecules. |
| ion | A species that has a charge. |
| ionic bond | The force of attraction between oppositely charged ions. |
| ionisation energy | The energy required to remove an electron from a gaseous atom. |
| isomers | Compounds with the same molecular formula but different properties. |
| isotopes | Atoms of the same element that have different numbers of neutrons. |
| Le Chateliers Principle | When one or more of the factors affecting the position of a chemical equilibrium change, then the equilibrium moves so as to oppose the change. |
| lone pair | A pair of electrons in the outer occupied energy level which are not involved in bonding. |
| kelvin | A unit of temperature. |
| mass number | The sum of the protons and neutrons in an atom. |
| mean bond enthalpy | The average bond energy for a particular bond in different compounds. |
| mechanism | The individual steps by which a reaction occurs. |
| metallic bonding | The force of attraction between the delocalised outer electrons and the resulting positive centres of the metal atoms. |
| molarity | The concentration of a solution in mol/dm3. |
| mole | The working quantitative unit used in calculations. One mole of a substance is the amount of that substance which contains as many particles as there are atoms in exactly 12g of carbon-12. |
| molecular formula | A formula which shows the actual numbers of atoms present in a molecule. |
| molecular ion | A molecule that has lost or gained electrons. |
| molecule | A compound formed by covalent bonding. |
| neutralisation | A reaction in which an acid and a base react together to form a salt and water. |
| noble gas | Any of the elements in Group 0 of the Periodic Table. |
| nuclear charge | The charge of the nucleus due to the number of protons present. |
| nucleophile | A species that can donate a lone pair of electrons to an electron-deficient carbon atom. |
| oxidation | A reaction in which a species loses electrons. |
| oxidation state (number) | The number of electrons of an atom used in forming bonds. |
| oxidising agent | An electron acceptor. |
| pascal | A unit pressure. |
| Periodic trend | A repeating pattern of properties shown by the elements in a Period of the Periodic Table. |
| polar bond | A covalent bond in which the pair of electrons are not shared equally. |
| polymer | A large molecule made by joining together many thousands of smaller molecules. |
| position isomers | Isomers in which the functional group is attached to different carbon atoms. |
| redox reaction | A reaction in which oxidation and reduction occur. |
| reducing agent | An electron donor. |
| reduction | A reaction in which a species gains electrons. |
| reflux | A method of prolonged heating without loss by evaporation. |
| relative atomic mass of an element | The average mass of an atom of an element (taking into account the natural occurrence of its isotopes) compared to 1/12th the mass of one atom of carbon-12. |
| relative molecular mass | The average mass of a molecule compared to the mass of one atom of carbon-12. |
| saturated compound | A compound in which the covalent bonds are all single bonds. |
| shielding | The effect of the inner electrons screening the outer electrons from the nuclear charge. |
| species | A general term used to denote an atom, an ion or a molecule. |
| standard solution | A solution whose concentration is known exactly. |
| stereoisomers | Molecules with the same structural formula which differ in the orientation of some atoms or groups of atoms. |
| structural formula | A formula which shows how the atoms are arranged in the molecule. |
| structural isomers | Molecules with the same molecular formula but with different arrangements of atoms within the molecule. |
| substitution | A reaction in which an atom or a group of atoms is replaced by a different atom or group of atoms. |
| transition metal | An element with partially filled d sub-levels in its atoms. |
| unsaturated compound | A compound containing one or more multiple covalent bonds. |
