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Chemical Bonding and Molecular Structure — Chemistry STD 11 Science — Question

Rajasthan BoardEnglish MediumSTD 11 ScienceChemistryChemical Bonding and Molecular Structure3 Marks
Question
Use molecular orbital theory to explain why the Be2 molecule does not exist.
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Answer

The electronic configuration of Beryllium is 1s22s2

The molecular orbital electronic configuration for Be2 molecule can be written as:

$\sigma^2_\text{1s}\ \ \sigma^.2_\text{1s}\ \ \sigma^2_\text{2s}\ \ \sigma^.2_\text{2s}$

Hence, the bond order for Be2 is $\frac{1}{2}(\text{N}_\text{b}-\text{N}_\text{a}).$

Where

Nb = Number of electrons in bonding orbitals

Na = Number of electrons in anti-bonding orbitals

$\therefore$ Bond order of Be2  $= \frac{1}{2}(4-4)=0$

A negative or zero bond order means that the molecule is unstable. Hence, Be2 molecule does not exist.

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