A chemical formula is a representation of how many atoms are in a substance. E.g. HCl Hydrogen Chloride 1 Hydrogen atom; 1 Chlorine atom 0 overall charge H Cl

H2SO4H2SO4 Hydrogen Sulfate 1 Hydrogen atom; 2 Sulfur atoms; 4 Oxygen atoms Small ‘subscript’ numbers tell us the amount of atoms for the atom to the left. E.g. O 4 = Oxygen x 4 0 overall charge O SO O O H H

SO 4 2- Sulfate ion 1 Sulfur atom; 4 Oxygen atoms Small ‘superscript’ numbers tell us the overall charge. E.g. 2- = two extra electrons 2- overall charge O SO O O [ ] 2-

NaCl Sodium chloride 1 Sodium ion; 1 Chloride ion Metal + Non-metal = Ionic bond 0 overall charge Na + Cl -