with opposite spins.atomic (proton) number the number of protons in the nucleus of an atom acid a species that is a proton donor.activation energy the minimum amount of kinetic energy that particles need to have in order to react when they collideaddition polymer a very long molecular chain formed by repeated addition reactions of many unsaturated alkene molecules (monomers).addition polymerisation the process in which unsaturated alkene molecules (monomers) add on to a growing polymer chain one at a time to form a very long saturated molecular chain (the addition polymer).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