Covalent Bonding
A covalent bond is a shared pair(s) of electrons.
Covalent bonds within molecules are strong, but they have weak intermolecular forces ( between molecules )
The formula for ionic compounds shows the ratio of elements in the compound. For example, NaCl tells us there is 1 sodium ion for every chloride ion.
The molecular formulae ( formula for covalent ) for simple molecular substances also shows the ratio, but it is the ratio of atoms within a single molecule. For example, NH3 tells us within an ammonia molecule there are 4 atoms; 1 nitrogen and 3 hydrogen.
Different models and their advantages/ limitations
Will come back to if have time, common sense