# How many pairs of electrons are shared between two adjacent carbon atoms in a saturated hydrocarbon?

May 1, 2016

How many pairs? Just the one.

#### Explanation:

Consider the ethane molecule, ${H}_{3} C - C {H}_{3}$. Each carbon atom has 6 electrons, 2 of which are inner core and are along for the ride. Thus, there are 4 electrons in the valence shell.

When carbon makes music with the hydrogen atom (1 electron), 2 electrons are conceived to form the $H - C$ bond. So far we have ${H}_{3} C \cdot$, a neutral carbon radical.

So the free electron on one carbon nucleus is conceived to couple to form a $C - C$ bond:

${H}_{3} C \cdot + \cdot C {H}_{3} \rightarrow {H}_{3} C - C {H}_{3}$

Of course, all of this is a formalism. But you can use this approach to assign formal charge.