C2 exists whereas Be2 does not exist.
It can be explained with the help of molecular orbital diagram.
C2-
6C = 2,4 = 1s2 , 2s22p2
6C = 2,4 = 1s2 , 2s22p2
Outermost molecular orbital configuration,
(π2px)2 = (π2py)2 , (σ2pz)0(π*2px)0
= (π*2py)0(σ*2pz)0
M.O. Diagram-
Bond order = \(\frac{n_b-n_a}{2}\) = \(\frac{2-0}{2}\) = 1
Since, its bond order is 1 so, C2 exists.
Be2
4Be = 2,2 = 1s2,2s2
4Be = 2,2 = 1s2 , 2s2
Outermost molecular orbital configuration
(σb2s)2(σ*2s)2
M.O Diagram –
Bond order = \(\frac{n_b-n_a}{2}\) = \(\frac{2-0}{2}\) = 0
Since, the bond order of Be2 is zero, so it does not exist as a molecule.
