Explain $\sigma$ and $\pi$ bonds,and mention the orbital overlapping involved in their formation.

(N/A) The covalent bond formed by the overlapping of atomic orbitals can be classified into two types:
$\sigma$-bond: This type of covalent bond is formed by the end-to-end (head-on) overlapping of two atomic orbitals along the internuclear axis. This is also known as axial overlapping. It occurs in the following ways:
- $s-s$ overlapping: Overlapping of two half-filled $s$-orbitals.
- $s-p$ overlapping: Overlapping between a half-filled $s$-orbital and a half-filled $p$-orbital.
- $p-p$ overlapping: Overlapping of two half-filled $p$-orbitals along the internuclear axis.
$\pi$-bond: This type of covalent bond is formed by the sidewise (lateral) overlapping of atomic orbitals. In this case,the axes of the overlapping atomic orbitals remain parallel to each other and perpendicular to the internuclear axis.