Covalent Bonds, the Octet Rule, Octet Rule exceptions and the Periodic Table

Dr. Walt Volland revised July 31, 2012 all rights reserved ©

The octet rule says "Main-group elements lose, gain or share electrons in such a way as to achieve an outer shell with eight electrons, ns2np6 that matches the nearest rare-gas (noble-gas) electron configuration."
Sodium with 11 electrons 1s22s22p63s1 loses one electron to form a Na+ cation with the electron configuration 1s22s22p6 which is [Ne] is neon core.


The combination of F and Cl gives FCl where both atoms have a complete octet.


Calcium with 20 electronshas an electron configuration [Ar]4s2. It loses two electrons to form a Ca2+ cation with the electron configuration for 18 electrons 1s22s22p63s23p6 which is an [Ar] core with 18 electrons.
Oxygen 1s22s22p4 gains two electrons to form an oxide O2- anion with the electron configuration 1s22s22p6 which is a [Ne] core with 10 electrons.
Chlorine 1s22s22p63s23p5 gains one electron to form chloride Cl1- anion with the electron configuration 1s22s22p63s23p6 an [Ar] core with 18 electrons..

Octet rule exceptions:

The octet rule really applies

to a limited number of elements in row 2 of the periodic table; C, N, O and F.  

Exceptions to the octet rule occur regularly for row 3 and greater.

These elements with open "d" subshells like phosphorus and sulfur do not always follow the rule. Examples of octet rule "violations" are SF6 and PCl5.Use the octet rule to predict the number of covalent bonds normally formed by phosphorus, P. Click for answer