Question

Use molecular orbital theory to explain why the \(Be_2\) molecule does not exist.

Answer 1

The electronic configuration of Beryllium is \(1s^2\; 2s^2\).

The molecular orbital electronic configuration for \(Be_2\) molecule can be written as:
\(\sigma^2_{1s} \sigma^{*2}_{1s} \sigma^2_{2s} \sigma^{*2}_{2s}\)
Hence, the bond order for \(Be_2\) is \(\frac{1}{2}(N_b-N_a)\)
Where, 
\(N_b\) = Number of electrons in bonding orbitals 
\(N_a\) = Number of electrons in anti-bonding orbitals
\(\therefore\) Bond order of \(Be_2\) =\(\frac{1}{2}(4-4)\) = \(0\) 
A negative or zero bond order means that the molecule is unstable. 

Hence, \(Be_2\) molecule does not exist.