Explain why helium molecule doesn't exist...(He2)...???
Each helium atom has two electrons in 1s-orbital and therefore, there are four electrons in He2 molecule. These electrons will be accommodated in si1ls and s*1s MOs as shown below.
The electronic configuration for helium molecule may be written as:
He2: (s1s)2 (s*1s)2
The zero bond order value indicates that there is no net bonding and He2 molecule should not be formed. In fact, there is no experimental evidence for the existence of this molecule.