Chapter U2.19, Problem 2E

Interpretation Introduction

Interpretation : Substances that one would expect to not have a smell are to be explained.

Concept Introduction :

Molecules smell differently. Humans are not able to smell some molecules. Some molecules are small and some are large; some are polar and some are nonpolar. Some molecules have metallic bonding while some have ionic bonding. Some molecules are made of metals while some are made of nonmetals or both metal and non-metal.

Answer to Problem 2E

Substances that one would expect to not have a smell are:

1. Those that are in solid/ liquid state
2. Those that have metallic, ionic and network covalent bonding
3. Small nonpolar molecules
4. Large sized molecules

Explanation of Solution

Given information:

Some molecules do not have smell.

Substances that one would expect to not have a smell are:

1. Those that are in solid phase- Molecules that can exist in gaseous form can be smelled easily as they can reach the receptor sites of our nose.The molecules exist in solid or liquid state and cannot be easily detected by the receptor sites.
2. Those that have metallic or ionic or covalent bonding- Molecules that have metallic, ionic or covalent bonding can exist only in solid state with the exception of mercury.These substances cannot easily form gases at room temperature. They cannot enter our nose and so cannot be detected by the receptor sites.
3. Small nonpolar molecules- Small nonpolar molecules like carbon dioxidedo not have smell.Non-polar molecules cannot bind to the mucous membrane of the receptor sites.
4. Large sized molecules- 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

Generally, solids, Small non-polar molecules and large sized molecules do not have smell.