the few exceptions on octet rule is that
In few compounds there is lesser number of electrons in the central atom (i.e less than eight). But still the compounds exist.For example:LiCl
In few elements there are more number of electrons than the octet rule.For example: PF5
In few compounds containing odd pair of electrons the electrons can be less than eight . For example in NO , N has lesser electtrons.
But still the compounds exist.