Question

dipole moment is cross product so why on decreasing bond angle dipole moment increases?

Answer 1

Electronegativity decides polarity of bond
Dipole moment decides polarity of molecule

For eg., If a molecule has 3 bonds ( Trigonal planar ) , polarity of each BOND will contribute to the overall polarity of the MOLECULE.
Each bond is a dipole (having positive charge at one end and negative charge at another )
Now let the dipole moment of first bond is P1 and that of second bond is P2 and that of third bond is P3
Now first we will add the dipole moments P1 and P2, for which we'll use UNDER ROOT P1 + P2 + 2P1P2 cos theta  [ where theta is the bond angle between bond 1 and 2 ]
and lower is the bond angle between them, higher will be the dipole moment !
hope this helps you out, If you're not satisfied, feel free to ask again :)

P.S. the resultant of P1 and P2 will be added to P3 to get overall dipole moment of the molecule !

Answer 2

Hii 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.