Explain the formation of $H_{2}$ and the energy level diagram of the $H_{2}$ molecule.

(N/A) The $1s$ atomic orbitals on two hydrogen atoms overlap to form two molecular orbitals,designated as $\sigma 1s$ and $\sigma^{*} 1s$.
$\sigma 1s$ is the bonding molecular orbital $(BMO)$ and $\sigma^{*} 1s$ is the antibonding molecular orbital $(ABMO)$.
The energy order is: Energy of $\sigma 1s < $ Energy of atomic orbital $1s < $ Energy of $\sigma^{*} 1s$.
The sum of the energies of the two molecular orbitals is equal to the sum of the energies of the two $1s$ atomic orbitals.
The energy level diagram for the formation of $H_{2}$ from two $H$ atoms is shown below.
$AO =$ Atomic orbitals,$MO =$ Molecular orbitals,$BMO =$ Bonding molecular orbital,$ABMO =$ Antibonding molecular orbital.
The formation of these molecular orbitals by the linear combination of atomic orbitals $(LCAO)$ is represented as:
$(i)$ $ABMO$ $(\sigma^{*} 1s)$: Formed by the subtractive overlap of two $1s$ orbitals.
(ii) $BMO$ $(\sigma 1s)$: Formed by the additive overlap of two $1s$ orbitals.