Oddo-Harkins rule

The Oddo-Harkins rule holds that elements with an even atomic number (such as carbon) are more common than elements with an odd atomic number (such as nitrogen).

This is because elements with odd atomic number have one unpaired proton and are more likely to capture another, thus increasing their atomic number. In elements with even atomic number, protons are paired, with each member of the pair offsetting the spin of the other, enhancing stability.

Oddo-Harkinsi reegel