Chem Defiintions

• Relative Atomic Mass


  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


  The energy required to remove an electron from each atom in one mole of gaseous atoms
• Bronsted-Lowry acid


  A species that is a proton donor
• Activation Energy


  The minimum energy required to start a reaction by the breaking of bonds
• Addition Polymerisation


  Formation of a very long molecular chain, by repeated addition reactions of many unsaturated alkene molecules (monomers).
• 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 solid is held to the surface of a solid, or, more rarely, a liquid
• Alicyclic


  Containing carbon atoms joined together in a ring that is not aromatic
• Aliphatic


  Containing carbon atoms joined together in straight or branched chains
• Alkali


  A type of base that dissolves in water forming hydroxide ions
• Alkanes


  The homologous series with the general formula CnH2n+2
• Amount of Substance


  The quantity whose unit is the mole
• Anhydrous


  A substance containing no water molecules
• Alkyl Group


  A side chain formed by removing a hydrogen atom removed from an alkane parent chain, for example, CH3, C2H5; any alkyl group is often shown as R.
• Anion


  A negatively charged ion
• Atom Economy


  (molecular mass of the desired product/sum of molecular masses of all products) x100
• Atomic Orbital


  A region within an atom that can hold up to two electrons, with opposite spins
• Atomic Number


  The number of protons in the nucleus of an atom
• Mean bond enthalpy


  The enthalpy change when one mole of gaseous molecules each breaks a covalent bond to form two free radicals, averaged over a range of compounds
• Avogadro Constant


  The number of atoms per mole of the carbon-12 isotope. (6.02 x 10^23)
• Base


  A compound that neutralises an acid to form a salt.
• Biodegradable Material


  A substance that is broken down naturally in the environment of a living organism
• Carbanion


  An organic ion in which a carbon atom has a negative charge
• Carbocation


  An organic ion in which a carbon ion has a positive charge.
• Catalyst


  A substance that changes the rate of a chemical reaction without it being used up
• Cation


  A positively charged ion
• Coordinate Bond


  A shared pair of electrons which has been provided by one of the bonding atoms only; also called a dative covalent bond.
• Covalent Bond


  A shared pair of electrons
• Cracking


  The breakdown of long-chained saturated hydrocarbons to form a mixture of shorter-chained alkanes and alkenes
• Curly Arrow


  A symbol used in reaction mechanisms to show the movement of an electron pair in the breaking or formation of the molecule
• Dative Covalent Bond


  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
• Displayed Formula


  A formula showing the relative positioning of all the atoms in a molecule and the bonds between them
• Disproportionation


  A redox reaction in which the same element is both oxidised and reduced
• Dynamic Equilibrium


  The equilibrium that exists in a closed system when the rate of the forward reaction is equal to the rate of the reverse reaction and concentrations do not change
• E/Z Isomerism


  A type of stereoisomerism in which different groups attached to each carbon of a C=C double bond may be arranged differently in space because of the restricted rotation of the C=C bond
• Electron Configuration


  A shorthand representation that shows how electrons occupy sub-shells in an atom
• Electronegativity


  A measure of the attraction of a bonded atom for the pair of electrons in a covalent bond