Chemistry iGCSE Definitions

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Diffusion - The equal spreading out of particles due to their energy

Electrolysis - A chemical change/decomposition caused by passing an electric current through an ionic substance which is either molten or in solution

Atom - The smallest part of an element which can exist whilst still retaining the properties

Molecule - 2 or more atoms covalently bonded together

Element - The simplest form of matter that cannot be created or broken down by any chemical means. It consists of only 1 type of atom

Compound - 2 or more element chemically combined together in a fixed ratio

Mixture - 2 or more elements/compunds mixed together, but not chemically combined, in any ratio

Relative Atomic Mass (Ar) - The weighted average mass of an atom of an element relative to 1 twelfth of a carbon12 atom

Homologous series - A series of organic compounds that have the same general formula, similar chemical properties and gradually changing physical properties

Hydrocarbon - A compound that contains ONLY hydrogen and carbon

Saturated - An organic compounds in which ALL the bonds are single bonds

Unsaturated - An organic compound that contains at least 1 carbon-carbon double bond

Isomer - Compounds with the same molecular formula but different structural formula

General formula - A formula that states the ratio of atoms of an element in the formula of every compound in a particular homologous series

Biodegradable - The ability for a molecule to be broken down by micro-organismst

Monomer - A molecule that can bind to other monomers to form a polymer

Polymer - A long chain of monomers joined together

Addition Polymerisation - A polymer which is formed when many monomers bond together without the loss of any atom or molecule

Condensation Polymerisation - A polymer formed when monomers combine and produce another small molecule such as water

Catalyst - A substance that increases the rate of reaction but is chemically unchanged at the end of the reaction

Activation energy - The minimum amount of energy required for a collision to be successful