Examples of MO Construction

This is a reducible representation of the point group which reduces to + Two molecular orbitals must be generated, one with and the other with (Ty symmetry. The two possible combinations are the bonding and antibonding orbitals which can be formed from the two Is atomic orbitals. 

The two electrons in the hydrogen molecule will occupy the lower energy bonding orbital, and none will go into the antibonding orbital. 

In the series from lithium through neon, similar symmetry considerations apply, except that in these examples the second electron shell must be considered. The two 2s orbitals, as was found to be the case for the two 1j orbitals, form MOs that possess and a symmetry. As regards the 2p orbitals, the two 2p orbitals lie along the molecular axis and belong to the same irreducible representation as the 2s orbitals. They also combine to give MOs that possess symmetry. 

The 2s and 2p orbitals of the same atom belong to the same irreducible representation of the point group. Their energies are also similar so they cannot be separated completely. Another way of making linear combinations is to first combine the 2s and 2p orbitals of the same atom 

The 2p and orbitals of the two atoms together form a representation that reduces to and tt . These correspond to two doubly degenerate it orbitals, one of which lies in the yz plane 

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