Oxygen is based on the Carbon nuclet in the initial ending configuration (gap) and has 2 deuterium building blocks on one side that both cap one valence connection point resulting in a valence of -2.

Oxygen can be seen as an alpha particle / helium nuclet that is added to the Carbon nuclet and it will form in this neutral ending shape. Reversed the effect is the release of alpha particles from heavier elements which is essentially releasing a group of 4 such as a neutral ending.