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Intermolecular Forces

Review - 2

Arrange the following molecules in order of increasing strength of intermolecular forces.

F2
Br2
Cl2
I2

Hints

First determine what type(s) of intermolecular force act between pairs of these molecules. These molecules are all diatomic (two atoms) and the two atoms in each molecule are identical. This should allow you to make a statement about whether they have permanent dipole moments. Then consider other types of intermolecular force.

Answer

These molecules are not polar. The only intermolecular forces acting between these molecules are dispersion forces. The size of the dispersion forces depends on the polarisability of the molecules which depends on the size of the molecules. The radius of the atoms in these molecules increases in the order F < Cl < Br < I (atomic radius increases down a group in the periodic table). This implies that the polarisability increases in the order F2 < Cl2 < Br2 < I2. The dispersion forces increase in the same order.

 

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