Write the formation of sigma covalent bond diagrammatically.

Explanation

It is a covalent bond formed by axial overlapping of half filled atomic orbitals along the internuclear axis.
Axial overlapping is also called end to end or head to head overlapping.
Example :
1. S-S overlapping : It involves overlap of two half filled s-atomic orbital. This occurs during the formation of H2 molecule. The bond is s-s s bond.

2. s-p overlapping : It involves overlap of half filled s orbital and half filled p-orbitals. This occurs during the formation of hydrogen halide molecule (HCl, HBr, Hl)