Question

Which molecule does not show zero dipole moment:
(A) $B{F_3}$
(B) $N{H_3}$
(C) $CC{l_4}$
(D) $C{H_4}$

Answer 1

In order to solve these types of questions we need to know the dipole moment and the factors affecting the dipole moment are the electronegativity and the distance is also the deciding factor for the dipole moment.

Complete step-by-step answer: For solving this question we need to know what is dipole moment so we have to know what is dipole moment .Dipole Moment : When two opposite charges are kept by a fixed distance then the dipole moment occurs. Then can occur in two ions due to ionic bond or between atoms due to covalent bond dipole moment also arises due to difference in electronegativity. The dipole moment is a measure of polarity in a molecule.Zero dipole moment is including the molecules like ${H_2},{N_2},C{l_2},$. But the zero dipole moment is not only due to non-polar bonds of zero electronegativity difference. Very few compounds are polar but have zero dipole moment due because they have symmetry.Now we will be checking the options one by one :So starting from $B{F_3}$ the net dipole moment of $B{F_3}$ is zero it is because all the F atoms are at equally angled so the net dipole moment is cancelled by it there is also not any lone pair and last it is non polar.Now we will be checking for $CC{l_4}$ so tetrachloromethane, has polar even but dipole moment is zero it is because of the shape of the molecule it is tetrahedral and it makes it very symmetrical and four polar bond each cancel each other out to produce zero dipole moment.Now moving on the $C{H_4}$ the dipole moment of of this molecule is zero it is because it has the tetrahedral geometry thus each bond is pair and at the symmetrically arranged hence each dipole moment of the molecule is balanced with each other.In tetra- atomic molecule such as $B{F_3}$ and $N{H_3}$ the dipole moment of $B{H_3}$ molecule is zero while that of $N{H_3}$ is 1.49D. The individual dipole moment of N-H bonds gives the resultant as 1.49 D.It is because due to the presence of the lone pair its geometry is distorted and the resultant is found not cancelled by the other.

Therefore option (B) is correct.

Note: According to hybridization the shape of the ammonia is should be tetrahedral due to lone pair and other three hydrogen atom in it but it was noticed that this is distorted due to the repulsion between the lone pair and the bonded electrons in the structure in ammonia.