Question

The chemical formula of acetylene is `C_2H_2`. What type of bond holds the two carbon atoms together?

Answer 1

A `C-=C` triple bond.

Explanation:

Each carbon contributes 4 electrons; each hydrogen contributes 2 electrons. A Lewis representation must therefore distribute 10 electrons: `2xxC-H` bonds, 4 electrons, and `1` `C-=C` triple bond, 6 electrons.

A valence bond formalism would gives rise to 2 `sp` hybrid orbitals on each `C` atom; one such hybrid interacts with `H` to form a `C-H` bond, and the remaining orbital forms a `C-C` bond. The remaining 4 electrons remain unhybridized and forms `pi` bonds above and below the plane of the `C-C` vector.