The Octet Rule: Help, Definition, and Exceptions

The Octet Rule is a general rule that is used to describe chemical bonding and draw Lewis Structures. The rule states that Main Group elements form bonds in a manner that results in each atom having eight valence electrons in the highest energy level (sometimes called outer shell). This results in each atom having the same electronic configuration as a noble gas.

For a complete tutorial drawing Lewis Structures, watch my video:

   • How to Draw Lewis Structures: Five Ea...  

The Octet Rule doesn’t work all the time and there are many exceptions. Hydrogen is one of the most notable exceptions and only needs two electrons to fill its outer shell. There are numerous other exceptions including expanded octets which can have up to twelve valence electrons.

Even with the exceptions, the Octet Rule is a valuable rule of thumb that helps scientists predict how atoms will bond to form compounds. These predictions are often what is ultimately unobserved in the lab.

Drawing/writing done in InkScape. Screen capture done with Camtasia Studio 4.0. Done on a Dell Dimension laptop computer with a Wacom digital tablet (Bamboo).