Question

why on decreasing bond angle dipole moment increases?

Answer 1

In multi atomic molecules, there may be a central positive charged atom and negatively charged atoms around it. Each of the chemical bonds will have a dipole moment associate with it.

Dipole moment is the product of distance d between the two atoms and charge q on them. This is a vector with the direction being : from -ve charge to positive charge. When there multiple bonds, usually they are inclined an some angles to the main axis of the molecule. Even otherwise, the net resultant dipole moment of the molecule is the vector sum of the individual moments.

If the angle of a bond is more, then its contribution to the vector sum will be less as the component value of the bond is p * cos Ф = q d cos Ф. The less the bond angle is, more the sum.

Answer 2

Hy I will help you ✌️

=> It is established the dipole moment is a result of multiplication of the magnitude of charges (Q) and the distance between them (r). What I understand is that when an electron and a proton get closer (bond length decreases), polarity decreases hence the dipole decreases. When they move further away from each other(bond length increases), the polarity increases and hence the dipole moment increases. However, in case of halides (H-X), let's take for example HF and HI, HF has a bigger dipole moment than HI, it is stated that the bond length of HF is smaller than HI.