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

The boiling points of the hydrogen halides are shown in the table.

Hydrogen halide	HF	HCl	HBr	HI
Boiling point / °C	+20	–85	–67	–35

Explain the trend in boiling points from $HCl$ to $HI$ .

Accepted Answer

The trend in boiling points increases from HCl to HI. This is because on going down group 17 in the Periodic Table, the number of electrons increases, thereby increasing the Instantaneous dipole-induced dipole forces of the respective halogens down the group. The Instantaneous dipole-induced dipole forces (id-id forces) between the respective molecules are increased with an increasing number of electrons of the atoms constituting the molecule. So, more energy is needed to change the liquid into vapour and the boiling point is higher in the case of HI compared to the HCl and HBr.

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.

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.

Lawrie Ryan and Roger Norris Solutions for Chapter: Chemical Bonding, Exercise 15: Questions

Lawrie Ryan Chemistry Solutions for Exercise - Lawrie Ryan and Roger Norris Solutions for Chapter: Chemical Bonding, Exercise 15: Questions

Questions from Lawrie Ryan and Roger Norris Solutions for Chapter: Chemical Bonding, Exercise 15: Questions with Hints & Solutions

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