The octet rule states that elements gain or lose electrons to attain an electron configuration of the nearest noble gas.
Incomplete Octet: There are certain atoms of certain elements that can exist in stable compounds forming bonds with less than eight valence electrons. When this occurs, the atom of the element within the molecule is said to contain an incomplete octet
Expanded octet: Expanded octet occurs when an atom is able to have more than 8 valence electrons.