Explain why \(BeH_2\) molecule has a zero dipole moment although the \(Be-H\) bonds are polar

Question

How many of the following compounds have zero dipole moment ?
\(NH_3, H_2O, HF, CO_2, SO_2, BF_3, CH_4\)

Answer 1

Concept Used:

Dipole moment of a molecule depends on both the polarity of bonds and the molecular geometry.

Explanation:

In the BeH₂ molecule, each Be–H bond is polar because beryllium and hydrogen have different electronegativities.

However, BeH₂ has a linear geometry with a bond angle of 180°.

The two Be–H bond dipoles are equal in magnitude but act in opposite directions along the same straight line.

As a result, the dipole moments of the two Be–H bonds cancel each other.

Conclusion:

Although the Be–H bonds are polar, the BeH₂ molecule has zero dipole moment due to its symmetrical linear structure.

Final Answer:

BeH₂ has zero dipole moment because the equal and opposite dipole moments of the polar Be–H bonds cancel each other.

Solution and Explanation