Chemistry – Ionic and covalent bonding, polymers and materials
Atoms and Compounds
Atomic number and mass number describe an atom: 
Compounds are when two are more atoms chemically join together – e.g. carbon dioxide – they are hard to separate
Isotopes: Isotopes are the different atomic forms of the same element, which have the same number of protons but a different number of neutrons – this means they will have the same atomic number (the same number of protons) but a different mass number
E.g. Carbon -12 and carbon-14 are a popular pair of isotopes