Question

Which of the following molecules have net dipole moments? For the polar molecules, indicate the polarity of each bond and the direction of the net dipole moment of the molecule.

_{$$\begin{gathered} {\text{a.CH}}_{2}C{l}_2,CHC{l}_3,CC{l}_4 \\ b.C{O}_2,N_{2}O \\ c.P{H}_3,N{H}_3 \end{gathered}$$}

Short answer

a. $C{H}_{2}C{H}_2$ and $CHC{l}_3$ have a net dipole moment because in these two molecules the polarity of opposite directions does not cancel each other.

$C{H}_{2}C{H}_2$

Tetrahedral molecular geometry

The electronegativity of all bonding atoms in dichloromethane are:

Hydrogen=2.2, carbon=2.5 and chlorine=3.1.

The electronegativity difference between C-H=0.3 and C-Cl=0.6. It proves that is polar.

The direction of the net dipole moment is toward the partially negative chlorine atoms.

$CHC{l}_3$

Tetrahedral molecular geometry

The electronegativity of all bonding atoms in dichloromethane are:

Hydrogen=2.2, carbon=2.5 and chlorine=3.1.

The electronegativity difference between C-H=0.3 and C-Cl=0.6. It proves that CHCl₃ is polar.

The direction of the net dipole moment is away from the slightly positive carbon atom to the slightly negative chlorine atoms but CHCl₃ is less polar than CH₂Cl₂ because of the presence of extra chlorine.

b)

$S{O}_2$is a nonpolar compound, because of its linear structure.

$S{O}_2$

It is a bent shaped molecule.

The electronegativity of all bonding atoms in Sulphur dioxide is as follows: Oxygen-3.44 and Sulphur-2.5.The difference in electronegativity between S-O=0.94.It proves that SO₂ is polar. Because of its bent direction they do not cancel each other and direction is away from partially positive sulphur toward the partially negative oxygen.

c)

$P{H}_3$

Bent shaped

The electronegativity of all bonding atoms in Sulphur dioxide is as follows: Phosphorus-2.1 and Hydrogen-2.1.

The difference between its electronegativity between P-H=0. It is a polar molecule because of the presence of lone pair electrons and electron-electron repulsion.

The direction of net dipole moment in PH₃ molecules is towards its lone pair electrons.

$N{H}_3$

Trigonal pyramidal

The electronegativity of all bonding atoms in Sulphur dioxide is as follows: Nitrogen-3.04 Hydrogen-2.1.

The difference between its electronegativity between N-H=0.84.It proves that this molecule is polar.

The direction of net dipole moment in PH₃ molecules is towards Nitrogen because it is more electronegative than that of hydrogen.

Step-by-step solution

Drawing Lewis's structure and molecular structure of the molecules.

Draw the lewis structure of the molecule with help of the octet rule which states that only the right electrons can be present in the outermost shell of elements and with the help of VSEPR theory find the molecular structure of molecules.

Find the electro negative and the direction of net dipole moment.

With the help of electronegativity of elements, find the difference between the electronegativity of the bonds and we all know that in polar molecules the direction of the net polar moment is towards more electronegative elements and in the case of lone pairs it is more electronegative than a normal carbon-hydrogen bond.