Bonding is the attraction between atoms.

There are two main types of bonding: covalent and ionic.

Covalent bonding is usually between two non-metals and is when electrons are shared.

Ionic bonding is when electrons are transferred from one atom to another which is usually between a metal and non-metal.

Both of these bonds make the atoms involved have full outer shells.

The more reactive a substance is, the easier it is to bond with another atom. This is because it has a low valency and therefore doesn't need to gain or lose many electrons.

The properties of ionically bonded substances:
Hard
Conduct heat and electricity (when molten or in solution)
High melting points

The properties of covalently bonded substances are:
Low melting point
Insulators of heat and electricity