18-electron rule

The 18-electron rule is a rule that tells us how many electrons should be in an atom or molecule to make it a stable molecule. We count how many electrons each atom has. Then, we add up the total number of electrons. If it is equal to 18, then the molecule is considered stable. For example, in a carbon dioxide molecule (CO2), there are 4 electrons from the carbon atom, and 8 electrons from the two oxygen atoms. When you add those two numbers together, you get 12 electrons. You would need 6 more electrons to follow the 18-electron rule.