Chapter U2.19, Problem 6E

Interpretation Introduction

Interpretation : The reason for the molecules having structure containing more than 20 carbon atoms to not have a smell is to be explained.

Concept Introduction :

Molecules smell differently. Humans are not able to smell some molecules because they are not recognized by the receptor sites in our nose. Some molecules are small, some are medium sized and some are large; some are polar and some are nonpolar.

Answer to Problem 6E

Molecules having structure containing more than 20 carbon atoms do not have a smell because they are large molecules. Carbon has a unique property. It bonds easily to other carbon atoms and forms long complex molecules. These long molecules cannot be detected by the nose.

Explanation of Solution

Size of the molecule plays an important role in smell. Small sized molecules have smell if they are polar. Molecules with carbon structure containing about 5 to 19 carbon atoms are considered medium sized molecules. Medium sized molecules have smell even if they are non-polar. Large molecules have more than 20 carbon atoms. Large sized molecules having 20 or more carbon atoms will not have any smell irrespective of whether they are polar or nonpolar because carbon bonds easily to other carbon atoms and forms long complex molecules. These long molecules cannot be detected by the nose.

Conclusion

Large sized molecules do not have smell due to long complex structures formed by carbon atoms.