$1 s$ atomic orbitals on two atoms (e.g. hydrogen form two molecular orbitals designated as $\sigma 1 s$ and $\sigma^{*} 1 s$ is.

$\sigma 1 s$ is bonding molecular orbital (BMO) and $\sigma 1 s$ is Antibonding molecular orbital (ABMO). Energy of

$\sigma 1 s$ is $<$ Energy of atomic orbital is $1 s<\sigma^{*} 1 s$.

(Energy of $\sigma 1 s+$ Energy of $\sigma^{*} 1 s$ ) $=($ Edition of energy of two $1 s)$

The energy diagram of $1 s, \sigma 1 s$ and $\sigma^{*} 1 s$ is as under.

Where, $\mathrm{MO}=$ molecular orbitals, $\sigma 1 s=\mathrm{BMO}$

$\mathrm{AO}=\text { Atomic orbitals, } \sigma 1 s=\mathrm{ABMO}$

Two $MO$, $\sigma 1 s$ and $\sigma^{*} 1 s$ are formed by overlapping of two $1 s$. Its figure is as under.