According to molecular orbital theory, electrons are considered as moving due to the influence of the atomic nuclei in the whole molecule.
Molecular orbitals are of two types, Bonding molecular orbital, and antibonding molecular orbital.
In the Bonding molecular orbital, electrons are considered to move between the nuclei of the two atoms. So, the electron density is high in the bonding molecular orbital.
It is formed by the addition overlap of atomic orbitals.
The energy of the bonding molecular orbital is lower than the combining atomic orbitals.
In anti bonding molecular orbital, electrons are considered to move outside the nuclei of the two atoms