A single covalent bond forms when two atoms share one pair of electrons.
Covalent bonds are formed between two or more atoms having zero or very small electronegativity difference. Such bonds exists between molecules of non-metals.
To form a covalent bond, each of the two participating atoms would put down an unpaired electron.
The unpaired electrons form a shared pair of electrons between them.
This shared pair of electrons constitutes the electron cloud that binds the two atoms together.
