Use molecular orbital theory to explain why the `Be_(2)` molecules do not exist?

Explanation

The electronic configuration of Beryllium is `1s^(2)2s^(2)`.
The molecular orbital electronic configuration for `Be_(2)` molecule can be written as :
`underset (1s)sigma^(2) underset(1s)sigma^(*2) underset(2s)sigma^(2) underset(2s)sigma^(*2)`
Hence, the bond order for `Be_(2)` is `(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)=(1)/(2)(4-4)=0`
A negative or zero bond order means that the molecules is unstable. Hence, `Be_(2)` molecule does not exist.