atom: atoms make up elements. Atoms consist of a nucleus of protons and neutrons with electrons orbiting the nucleus in shells.
element: a basic substance that is only made up of one type of atom. It cannot be separated by chemical means.
ion: an atom or molecule with an electric charge due to loss or gain of electrons.
molecule: two or more atoms chemically bonded together (eg. H20, CO2)
compound: a material made of atoms of two or more different elements.
empirical formula: a formula that gives the proportion of elements present in a compound but not the actual numbers or arrangements.
molecular formula: a formula which states the number and type of atoms present in a molecule of a substance.
