Chapter 8, Problem 127A

Interpretation Introduction

Interpretation:

The polar molecules need to be determined.

Concept introduction:

The bond formed between two atoms having a large electro negativity difference is polar. This is becausethe difference in electro negativity creates partial negative and positive charges on the atoms. The more electronegative atom gets a partial negative charge and a less electronegative atom gets a partial positive charge.

A covalent bond can be polar in nature if the difference in electro negativity value falls in the range of 0.6-1.9.

All the ionic bonds are polar in nature with the value of electro negativity difference more than 1.9.

Also, the overall molecule can be polar or non-polar depending on the overall dipole moment. A molecule having polar bonds can be overall non-polar if all the dipole moments get canceled out.

Answer to Problem 127A

${\text{CH}}_{\text{3}}\text{Cl}$, $\text{CIF}$ and ${\text{NCl}}_{\text{3}}$ are polar compounds.

Explanation of Solution

Given Information: The given molecules are as follows:

${\text{CH}}_{\text{3}}\text{Cl}$, $\text{CIF}$, ${\text{NCl}}_{\text{3}}$, ${\text{BF}}_{\text{3}}$ and ${\text{CS}}_{\text{2}}$

Reason for correct options:

The given molecule is ${\text{CH}}_{\text{3}}\text{Cl}$.

Here, the electro negativity of Cl is 3.16 and that of C is 2.55. The difference in electro negativity is 0.61. Thus, the C-Cl bond is polar in nature. The electro negativity difference of C and H is not that much thus, it has a non-polar covalent bond.

The Lewis structure is represented as follows:

The direction of the dipole moment is towards Cl atom and it does not get canceled out thus, the overall molecule is polar in nature.

Now considering ClF,

Here, Cl-F bond isa polar bond as the electro negativity of Cl and F is 3.2 and 4 respectively.

The electronegative difference is 4-3.2 = 0.8 which is more than 0.6.

There is no other bond in the molecule. Therefore, CIF is a polar molecule.

Considering the NCl₃molecule.

The Lewis structure is represented as follows:

The electro negativity of N and Cl is 3.07 and 2.88 respectively. The electro negativity difference will be 0.19 which is very small thus, the N-Cl bond is not polar. But, there is one lone pair of electron on the N which makes the overall molecule polar as the electron density is more where the lone pair is present.

The direction of the dipole is towards lone pair making the molecule slightly polar in nature.

Conclusion

Reason for incorrect options:

Considering ${\text{BF}}_{\text{3}}$ molecule, the electro negativity of B and F is 2.04 and 3.98. The difference is 1.94 making B-F bond polar in nature.

The Lewis structure is represented as follows:

The above molecule is symmetrical and planar in nature thus, dipole moments get canceled out and the overall molecule is non-polar.

Considering ${\text{CS}}_{\text{2}}$ molecule, the electro negativity of C and S is 2.55 and 2.58. The difference is very low thus, the bond is non-polar covalent.

The Lewis structure is represented as follows:

The molecule is linear and both S atoms have the same number of lone pairs of electrons thus, the overall molecule is non-polar in nature.