Ncert Exercises & Solutions

4.22 Explain why BeH $_{2}$ molecule has a zero dipole moment although the Be–H bonds are polar.

The Lewis structure for BeH $_{2}$ is as follows:

There is no lone pair at the central atom (Be) and there are two bond pairs. Hence, BeH $_{2}$

is of the type AB $_{2}$ . 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, BeH $_{2}$ molecule has zero dipole moment.