Question

Put the following molecules in order from lowest to highest overall net dipole moment and explain why.

a. NH3

b. HCl

c. HF

d. CCl4

Answer 1

The order from lowest to highest overall net dipole moment is

CCl₄ < HCl < NH₃ < HF

In CCl₄ the C-Cl bond dipole moments cancel each other in the molecule due to regular tetrahedran geometry. Hence the net dipole moment is Zero which is the lowest.

Due to high electronegativity H-F dipole moment is much higher than H-Cl and N-H bonds hence HF must have the highest dipole moment.

Between HCl and NH₃ , in NH₃ molecule there are three N-H bonds in a pyramid geometry will add up in the vector addition to give a net higher dipole moment than that of HCl.

Hence the dipole moment of NH₃ is higher than that of HCl.

[ Dipole moment is the measure of polarity. It is measured as = charge x distance. = Qd C-m

Its unit is C-m , but usually expressed as Debye unit 1 Debye unit = 3.336 x 10^-30 C-m

= Qd / [3.336 x 10^-30 ] D

where Q is the partial charge developed due to difference in electronegativity of the bonding elements.

The net dipole moment of a molecule is the vector sum of all the individual bond dipole moments.]