Question

Can someone explain zero permanent dipole moment in the gas phase and which of these have zero permanent dipole moment?
BeH2, CH4, NH3, H2O, HF

Answer 1

requirement of polarity we got to have geometrical asymmetry. such as CH4, its tetrahedrally molecules have polar bonds but the molecules themselves are not polar because the symmetry of bonds cancels out the retricemetry of charges.
same goes to lineary shaped molecules. so BeH2 is non polar.
H2O is a polar molecule because if we draw a lewis structure, central atom is the most electronegative element. we have 2 lone pairs and 2 pairs of bonded electrons. water is a polar molecules because of the difference on how the electrons are distributed and has a dipole moment.
look at NH3 geometrical shape, it has a lone pair at the top and 3 shared pair of electrons its retricemetricals so its polar and has a dipole moment.
H-F hydrogen bond occurs between hydrogen and a highly electronegative elements and has 3 pairs of active lone pairs so of course it has a separation of charges.

Answer 2

Thank You!!

Answer 3

Your most welcome :)