What's a molecule that is an exception to the octet rule, and why is it considered an exception?
One chemical that is an exception to the octet rule is BCl3, or boron trichloride. Boron is a group 13 element, meaning it has 3 valence electrons. So each of these three valence electrons forms a single bond with a chlorine atom. This gives a total of 3*2=6 electrons surrounding boron, which is two less than the standard octet. As a result, BCl3 is a highly reactive compound and it acts as a Lewis acid, meaning that it readily accepts a pair of electrons from an electron donor to make an octet.