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



Due to sp hybridization shown by Be in Be${{H}{2}}$ the molecule Be${{H}{2}}$ is linear. Though the individual Be-H bonds are polar (due to difference of electronegativity) yet Be${{H}_{2}}$ has a dipole moment of zero as dipole moment is a vector quantity (it has both magnitude and direction). The individual polar character of Be-H bond cancels out as the dipoles are equal and opposite as shown below :