Chapter U2.18, Problem 7E

Interpretation Introduction

Interpretation : Reason for dimethyl sulfide to be added to natural gas that is used in homes and buildings is to be explained.

Concept Introduction :

There are two classes of molecules; polar and nonpolar. Asymmetrical molecules are polar. Diatomic molecules are nonpolar. Some molecules are symmetrical in shape. The symmetry in their shape makes them nonpolar even though they have polar bonds within them. Polar molecules have smell while nonpolar molecules do not have smell.

Explanation of Solution

In methane molecule, the polarities of the individual polar bonds balance each other out due to the shape of the molecule. There is no partial positive or negative charge on the molecule. So the overall molecule is nonpolar. Hence methane has no smell.

The natural gas that is supplied to our homes and buildings is mainly composed of methane. Any kind of leakage of this gas can cause explosion and is very dangerous. Since methane has no smell, it would go undetected in case of any leakage. Dimethyl sulfide has a smell as it is a polar molecule. It is asymmetrical in shape so it has smell. It can be easily detected by our nose. It is added to natural gas so that the leakage can be easily detected and accidents can be prevented.

Conclusion

Methane is a nonpolar molecule even though its bonds are polar, as the two pairs of dipoles cancel out each other and there is no net charge on the molecule. Hence it has no smell too.