Carbon’s reactivity is driven by the quest for a filled outer shell. However, forming C⁴⁻ or C⁴⁺ ions is unfavorable due to the challenges associated with holding or removing four electrons, making such ion formation energetically impractical for carbon.

Carbon addresses the electron gaining or losing challenge by sharing valence electrons with other atoms, a strategy also adopted by various elements to form molecules through the sharing of electrons.

Hydrogen, with one electron in its K shell, shares electrons with another hydrogen atom to form H₂. This sharing allows both hydrogen atoms to attain the electronic configuration of the nearest noble gas, helium.

A single covalent bond is formed when two atoms share a pair of valence electrons. This shared pair constitutes the bond, enabling both atoms to achieve a stable noble gas configuration in their outermost shells.

The electronic configuration of chlorine is 2, 8, 7. Its valency is 1, as chlorine requires one more electron to complete its outer shell.