The dipole moment of a molecule is a measure of the net charge separation within the molecule. In beryllium hydride (BeH2), the bonds between beryllium and hydrogen are polar due to the difference in electronegativity between the two atoms. Beryllium is less electronegative than hydrogen, so the electrons in the Be-H bonds are pulled towards the hydrogen atoms, creating a partial positive charge on beryllium and a partial negative charge on hydrogen.

However, beryllium hydride is a linear molecule, which means that the dipole moments of the two Be-H bonds cancel each other out. This is because the dipole moments of the two bonds are equal in magnitude but opposite in direction. As a result, the net dipole moment of beryllium hydride molecule is zero.

In general, the dipole moment of a molecule is determined by the polarity of the bonds and the geometry of the molecule. If the molecule is symmetrical, the dipole moments of the individual bonds will cancel each other out and the net dipole moment will be zero.