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Question 22

Explain why BeH2 molecule has a zero dipole moment although the Be–H bonds are polar.

Answer

The molecule with symmetrical & linear geometries have zero dipole moment because they  are vector in nature & the dipole of different bonds cancel with one another & in a unsymmetrical molecule & bent geometries, the geometries have specific dipole moment because the bond polarities do not cancel each other.

The Lewis structure for BeH2 is as follows:

Since there is no lone pair at the central atom (Be) and there are two bond pairs, BeH2 is of the type AB2. It has a linear structure.



Dipole moments of each H–Be bond are equal and are in opposite directions. Therefore, they nullify each other. Hence, BeH2 molecule has zero dipole moment.

While in Be---H , dipole moment of Be  & H are not equal & they donot nullify each other.hence has a specific dipole moment.

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