Question

He ion has less stable arrangement that H2 molecule. Explain using molecular orbital
theory.

Answer 1

configuration of He
sigma 1s^2, sigma* 1s^2,

bond order =(bonding orbital electron-antibonding orbital electrons )/2
=(2-2)/2=0

hence bond order =0

configuration of H2
sigma 1s^2 , sigma* 1s^0
bond order =(2-0)/2=1

we know according to molecular orbital theory .
if bond order of any molecule is zero or negative then that molecule is unstable.
above we see bond order of He is zero so, this is unstable .but H2 bond order is positive hence this is stable .
we also say that He is less stable then H2 molecule