# Two carbon atoms held together in a double covalent bond share how many electron?

A $C = C$ bond is composed of 4 electrons.
Consider ethylene, ${H}_{2} C = C {H}_{2}$. Each hydrogen atom has the one electron available for bonding. Each carbon atom has 4 electrons available for bonding. (The remaining electrons $C , Z = 6$ are inner core, and are not presumed to be involved in bonding.)
So in a olefin bond $C : + : C$ gives the $C = C$ junction.