Multiple Bonds
When atoms of Group VA or Group VIA react with each other or themselves there are not enough electrons to share to form a single covalent bond that will satisfy the octet rule.  However there is no reason that we have to restrict the bonding in the compound to a single bond.  Elements like N tend to form triple bonds.

                                                         : N      N :

Notice that in a Lewis diagram the three shared electrons are placed between the two atoms.  We count all of these electrons as though they belong to both of the atoms. Each nitrogen therefore has an octet.  The triple bond is usually represented by three dashes, so the bonding N2 molecule is normally shown as

                                                         : N      N :

Double bonds are also possible.    For example the molecule CO2 contains two sets of double bonds.

                                                     : O :: C :: O :
                                                        ..             ..