The boiling points of the halogens are: Describe the trend in these boiling points going down Group 17.

The trend in these boiling points, increases on going down Group 17.

The trend in these boiling points, de cre ases on going down Group 17.

The boiling points of the halogens are: Explain the trend in these boiling points.

The trend in these boiling points increases on going down Group 17. 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 atoms are increased with an increasing number of electrons. So, more energy is needed to change the liquid into vapour and the boiling point is higher in the case of Iodine compared to the other halogens which are above Iodine in group 17. 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 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.

E M B I B E

Chemistry for Cambridge International AS & A Level Coursebook with Digital Access (2 Years)>Chapter 4 - Chemical Bonding>Questions

Lawrie Ryan and Roger Norris Solutions for Chapter: Chemical Bonding, Exercise 12: Questions

Author:Lawrie Ryan & Roger Norris

Lawrie Ryan Chemistry Solutions for Exercise - Lawrie Ryan and Roger Norris Solutions for Chapter: Chemical Bonding, Exercise 12: Questions

Attempt the free practice questions on Chapter 4: Chemical Bonding, Exercise 12: Questions with hints and solutions to strengthen your understanding. Chemistry for Cambridge International AS & A Level Coursebook with Digital Access (2 Years) solutions are prepared by Experienced Embibe Experts.