use the M.O theory, explain why Be2 molecule does not exist?

Be2 is unstable and does not exist in nature as it has zero bond order.

The electronic configuration of Be2 is ( s 1s)2 ( s *1s)2 ( s 2s)2 ( s *2s)2.

We are showing below the molecular orbital diagram for Be2.




Now ,  

where Na and Nb are the number of electrons present in bonding and antibonding molecular orbitals respectively.


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Each Beryllium has 4 electrons, and two orbitals.Combining two Beryllium atoms would result in a total of four orbitals and eight electrons.Each 1s orbital would combine with the other 1s orbital corresponding to the other Beryllium. Likewise the 2s orbitals would combine.Each would form a bond and an anti-bond.Thus having two bonds and two anti-bonds, you would fill in the eight electrons, knowing that there are a maximum of two for each orbital.All orbitals are filled, which means that there is as much anti-bonding as there is bonding interactions between the two.

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