91Ó°ÊÓ

The boiling points of compounds depend upon the type of intermolecular interactions and their surface area.

• Ionic compounds have higher boiling points because of very strong interactions of the interionic forces as compared to covalent compounds.
• The boiling points of covalent compounds depend upon the kind of functional groups present in the compounds.
• The Van der Waals forces of attraction are weaker than the dipole-dipole interactions.Hydrogen bonding is the strongest among the intermolecular interactions, whereas Van der Waals forces are the weakest.
• The compounds witha larger surface area have higher boiling points.The compounds having greater polarizability have higher boiling points.

a. The given compounds are 2-methyl propene and propanone.

2-methyl propene

Propanone

Propanone will have a higher boiling point because of the stronger intermolecular forces. Due to the presence of a polar carbon-oxygen bond, this compound will have a net dipole moment.

There are dipole-dipole interactions and Van der Waals forces of attraction in the propanone.

On the other hand, 2-methyl propene will have only weak Van der Waals forces of attraction.

b. The given compounds are propanoic acid and methyl-ethanoate.

Propanoic acid

Methylethanoate

Out of these two compounds, propanoic acid will have a higher boiling point. This is because of the presence of strong intermolecular interactions.

Propanoic acid has Van der Waals forces due to the presence of the alkyl group. It also has strong dipole-dipole interactions due to the presence of a polar C-O bond. It is also capable of showing hydrogen bonding.

Conversely, methyl ethanoate has a low boiling point because it is not capable of forming hydrogen bonds.

Hexane

Heptane

Heptane will have a higher boiling point as compared to hexane. This is because heptane is a larger molecule as compared to hexane; larger molecules have higher boiling points due to the presence of a larger surface area.

Heptane will have more surface area than hexane. As a result, heptane will have a higher boiling point.

Vinyl chloride

Vinyl iodide

Vinyl iodide will have a higher boiling point because of the high polarizability of the iodine atoms compared to chlorine.