Name: Structure of Xenon-oxygen Compounds
Uploaded: 2019-07-19
Duration: 6 min 14 s
Description: Noble gases, also called inert gases because of their least reactivity, still react with one of the most reactive elements, i.e., oxygen, to form different c...

Question

Bromine,

{Br}_{2}

, and iodine monochloride,

ICl

, have the same number of electrons. But the boiling point of iodine monochloride is nearly 40

°

C higher than the boiling point of bromine. Explain this difference.

Accepted Answer

Instantaneous dipole-induced dipole forces (id-id forces) increase with:
• increasing the number of electrons (and protons) in the molecule.

• increasing the number of contact points between the molecules: contact points are places where the molecules come close together.

Although the number of electrons is equal for both bromine and iodine monochloride, the number of contact points between the iodine monochloride molecules is more than bromine.

The molecules in iodine monochloride can line up beside each other. So there are many contact points in iodine monochloride than that of the bromine. Thus, the id-id forces are higher in iodine monochloride. So the boiling point is higher in the case of butane.

The molecules of bromine will be more compact than iodine monochloride. The surface area available for coming into contact with neighbouring molecules will be smaller and hence, the id-id forces are relatively lower for bromine. So the boiling point is lower for bromine. Thus, iodine monochloride will have a higher boiling point than bromine.

Instantaneous dipole-induce dipole forces (id-id forces): The electron charge clouds in a non-polar molecule (or atom) are constantly moving. It often happens that more of the charge cloud is on one side of the molecule than the other. This means that one end of the molecule has, for a short time, more negative charge than the other. A temporary dipole is set up. This dipole can set up (induce) a dipole on neighbouring molecules. As a result of this, there are forces of attraction between the $δ +$ end of the dipole in one molecule and the $δ -$ end of the dipole in a neighbouring molecule. These dipoles are always temporary because the electrons clouds are always moving. Instantaneous dipole-induced dipole forces are sometimes called temporary dipole-induced dipole forces. These forces are also called London dispersion forces. It is the weakest intermolecular attractive force.

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