The amount of bonds in covalent bonding?

It's to make them stable, here is a copy of the periodic table a href="http://www.bartleby.com/images/A4images/A4elemen.jpg" rel="nofollow"http://www.bartleby.com/images/A4images/…/a as you can see oxygen is in group 6 so needs to form 2 bonds to make 8 outer electrons. Nitrogen is in 5 so needs 3 bonds to get 8 electrons. This is to stop free radicals forming or a lone pair of electrons as these are unstable.