Question

The electronic configuration of Be$_2$ molecule according to MOT is

• A. (\(\sigma 1s^2\)) (\(\sigma^* 1s^2\)), (\(\sigma 2s^2\)), (\(\sigma^* 2s^0\))
• B. (\(\sigma 1s^2\)) (\(\sigma^* 1s^2\)), (\(\sigma 2s^2\)), (\(\sigma^* 2s^2\))
• C. (\(\sigma 1s^2\)) (\(\sigma^* 1s^2\)), (\(\sigma 2s^1\)), (\(\sigma^* 2s^2\))
• D. (\(\sigma 1s^2\)) (\(\sigma^* 1s^1\)), (\(\sigma 2s^2\)), (\(\sigma^* 2s^2\))

Hint:

In molecular orbital theory, the electron configuration for homonuclear diatomic molecules like Be$_2$ is determined by filling bonding and antibonding orbitals in order of increasing energy.

Answer 1

The Correct Option is B

Step 1: Understanding Molecular Orbital Theory (MOT).
According to MOT, the electronic configuration of molecules is determined by the combination of atomic orbitals to form molecular orbitals. For Be$_2$, the bonding molecular orbitals are filled first, followed by the antibonding orbitals.
Step 2: Analyzing the options.
(A) (\(\sigma 1s^2\)) (\(\sigma^* 1s^2\)), (\(\sigma 2s^2\)), (\(\sigma^* 2s^0\)): This is incorrect because the antibonding \(\sigma^* 2s\) orbital should be filled.
(B) (\(\sigma 1s^2\)) (\(\sigma^* 1s^2\)), (\(\sigma 2s^2\)), (\(\sigma^* 2s^2\)): This is the correct configuration for Be$_2$, with both the bonding and antibonding orbitals filled as per MOT.
(C) (\(\sigma 1s^2\)) (\(\sigma^* 1s^2\)), (\(\sigma 2s^1\)), (\(\sigma^* 2s^2\)): This is incorrect because Be$_2$ does not have an unpaired electron in the \(\sigma 2s\) orbital.
(D) (\(\sigma 1s^2\)) (\(\sigma^* 1s^1\)), (\(\sigma 2s^2\)), (\(\sigma^* 2s^2\)): This is incorrect because the \(\sigma^* 1s\) orbital cannot have only one electron.
Step 3: Conclusion.
The correct electronic configuration for Be$_2$ according to MOT is (B).