Question

Halocarbons form by substituting a hydrogen atom of an alkane molecule with elements from the halogen group. Halocarbons have different boiling points than the original alkane molecules. Arrange the halocarbons in increasing order of their boiling points. Refer to the periodic table if needed.

Answer 1

Here we have to arrange the halohydrocarbons in increasing order of their boiling point with reference to the periodic table.

The increasing order of boiling points of halohydrocarbons will be R-I > R-Br> R-Cl > R-F.

When we go down in the halogen series of the periodic table i.e. F→Cl→Br→I the size and atomic weight increases and also the polarisibility increases. In chlorine (Cl) due to small size the the formation of dipole is less than bromine (Br) and iodine (I). The boiling point of the halohydrocarbon depends upon the stronger inter-molecular force of attraction.

As the dipole moment of the R-I (where R is the alkyl group) is more than the R-Br and R-Cl the intermolecular force of attraction will be high for R-I thus we find high boiling point.

Henceforth the increasing series of boiling point of halohydrocarbons are-       R-I > R-Br> R-Cl > R-F.