δ+ and δ- indicate positive and negative charges, which are separated by distance d. These charges are equal in magnitude but opposite in sign.
1. In the diatomic molecule of HCl, dipole moment of HCl molecule is same as dipole moment of HCl bond, which is 1.03D.
2. In beryllium fluoride molecule, the dipole moment is zero. BeF2 has a linear shape. There exist two individual bond dipole moments, which cancel each other resulting in the net dipole moment zero. This is because in BeF2 molecule, the bond dipole moments are equal in magnitude and opposite in direction.
3. In the triatomic CO2 (carbon dioxide) molecule, the dipole moment is zero. Due to the linear structure of the molecule, the dipole moment of C=O bond (2.3D) on one side of the molecule gets cancelled by that on the other side of the molecule, resulting in net zero dipole moment.
4. In triatomic H2O water molecule, the dipole moment is 1.84D. Due to the bent structure of the water molecule, the dipole moment is not zero. This is due to the resultant dipole moments of 2 O-H bonds, inclined at 104.5 degrees, with 2 lone pairs on oxygen atoms.
5. In tetra-atomic boron trihydride (BH3), the dipole moment is zero, but that of ammonia (NH3) is 1.49D. This is because BH3 has a symmetrical structure and the 3 B-H bonds are placed at an angle of 120 degrees to each other. As the 3 bonds are in a single plane, dipole moments cancel each other, with net dipole moment equal to zero. On the other hand, NH3 has a pyramidal structure, with 3 N-H bonds and a lone pair on nitrogen atom. This gives the resultant dipole moment as 1.49D.
Also, when we consider NH3 and NF3 molecules, both have with 3 N-H bonds and a lone pair on nitrogen atom but the resultant dipole moment of NF3 is less than that of NH3. This is because the dipole formed between the lone pair and nitrogen atom differs in both NH3 and NF3 molecules. Fluorine, being more electronegative than nitrogen, will attract all the shared electrons towards it from nitrogen in opposite direction to net dipole moment. Thus, the resultant dipole moment of NF3 decreases. While nitrogen being more electronegative than hydrogen, it will attract all the shared electrons towards it from hydrogen in same direction to net dipole moment due to N-H bonds. Thus, the resultant dipole moment of NH3 increases.
6. In CH4 (methane) and CCl4 (carbon tetrachloride) molecules, the dipole moments are zero. These two, CH4 and CCl4 molecules, have symmetrical tetrahedral shape. Therefore, dipole moments of C-H bonds in CH4 cancel out each other and result in zero dipole moment, same in CCl4 molecule dipole moment of C-Cl bonds cancel out each other and result in zero dipole moment.