(Polar molecules, Non-polar molecules, etc.)
Although most elements need exactly 8 electrons in a bond to be stable, there are some exceptions to the rule. Some elements, like Boron, can be stable with less than 8 electrons, while some other elements, like Sulfur, can be stable with more than 8 electrons. This is due to the expansion of valence that occurs which allows certain elements, like sulfur, to utilize their empty d-orbitals to hold more electrons. In this case, sulfur is using its empty 3D orbital to allow itself to fit up to 12 electrons rather than only 8.
I just got out of lecture. Lavelle said that certain atoms can break the octane rule. P, Cl, and S can accommodate more than 8 valence electrons. Atoms in period 3 or higher have higher d-orbitals (I'm literally coping my notes so if this is really brief that is why).
To add on to the other replies, P, Cl, and S can bond up to 6 times because they can utilize their empty 3d orbitals. 2p elements aren't able to do this because there aren't any 2d orbitals. I'm pretty sure that other elements with empty d orbitals can also bond more than 4 times.