Octet Rule

Introduced to this in AP Chemistry

Incomplete Octet: H, Be, B

Expanded Octet: Metalloid / Nonmetal elements in 3rd period and beyond

4 elements HAVE to have an octet: Carbon (C), Nitrogen (N${}_2$), Oxygen (O${}_2$), Fluorine (F)

Rules §

1. Give all atoms an octet
2. Place remaining pairs on 3rd period (& below) element - typically central atom

Exception to Octet Rule §

Row 3 and heavier nonmetals can have more than  electrons around them when they have to. Row 3 and heavier elements have empty orbitals that are close in energy to valence and orbitals. These empty  orbitals can accept extra electrons.