Question

Predict which will have the higher boiling point: ICl or Br₂.Explain your reasoning.

Short answer

The boiling point of ICl is more thanBr₂ due to a stronger force of attraction between the ICl molecules, i.e. dipole forces, compared toBr₂, which has only dispersion forces.

Step-by-step solution

Define polarizability

A molecule with a charge cloud that is easily distorted is said to be very polarizable and will have large dispersion forces; one with a charge cloud that is difficult to distort is not very polarizable and will have small dispersion forces.

 Identify the name of the compound

The compound given are\({\rm{Cl}}\)and\({\rm{B}}{{\rm{r}}_2}\)

Since there is\(1{\rm{Br}} - {\rm{Br}}\)a bond only in\({\rm{B}}{{\rm{r}}_2}\)with no electronegativity difference.

Hence there is 0 dipole moment in\({\rm{B}}{{\rm{r}}_2}\)

Hence the molecule\({\rm{B}}{{\rm{r}}_2}\)is non-polar.

And in\({\rm{ICl}}\), there is\({\rm{I}} - {\rm{Cl}}\)a bond with electronegativity difference between\({\rm{I}}\)and\({\rm{Cl}}\).

Hence the dipole moment of the molecule |C| is not 0.

Hence the molecule\({\rm{ICl}}\)is polar.

Since the polar molecule will have the dipole-dipole force of attractions while the non-polar molecule will have only dispersion forces.

And since the strength of dipole-dipole forces is much more than dispersion forces.

Hence more energy will be required to overcome the dipole-dipole force of attractions in ICI molecules compared to\({\rm{B}}{{\rm{r}}_2}\)molecules and evaporate them.

Hence the boiling point of ICl is more than \({\rm{B}}{{\rm{r}}_2}\)due to a stronger force of attraction between the ICl molecules, i.e. dipole forces, compared to\({\rm{B}}{{\rm{r}}_2}\) which has only dispersion forces.