1. Melting and Boiling points?
Group 7 non-metals
Trends
Halogens
Melting and Boiling points?
Reactivity…
Densities

2. Why are they called the ‘halogens’?
Halogens are very reactive non metals.
They are all toxic or harmful because they are so reactive. Before antiseptics, iodine was used to clean wounds as it is harmful to all things, including bacteria.
They are also never found free in nature because of their reactivity – they are found as compounds with metals.
Photo credit: Dr John Mileham
Liquid bromine in a jar on the left, iodine on the right.
These halogen-metal compounds are salts, which give halogens their name – ‘halo-gen’ means ‘salt-former’.

3. What are the general properties of the halogens?
All the halogens are:
non-metals and so do not conduct electricity
brittle and crumbly when solid
poisonous and smelly.
They become darker in colour down the group:
is pale yellow
is yellow-green
is red-brown
is grey

4. Halogens – what do they look like?
Chlorine Bromine
Iodine

5. How do halogen molecules exist?
All halogen atoms require one more electron to obtain a full outer shell and become stable.
Each atom can achieve this by sharing one electron with another atom to form a single covalent bond. +  F
This means that all halogens exist as diatomic molecules: F2, Cl2, Br2 and I2.

6. General trends Densities and melting points increase down group
NB: There are quite a few exceptions to this trend.

7. What is the physical state of the halogens?
The melting and boiling points of the halogens increase down the group, as the molecules become bigger.
Halogen
Relative size
Melting point (°C)
Boiling point (°C)
State
-220
-118
gas
-101
-34
gas -7 59
liquid
114
184
solid
What is the state of each halogen at room temperature?

8. General Reactive trends
Non-metals getting more reactive
Fluorine – the most reactive non-metal

9. How does electron structure affect reactivity?
The reactivity of halogens decreases going down the group. What is the reason for this?
The atoms of each element get larger going down the group. F
decrease in reactivity
This means that the outer shell gets further away from the nucleus and is shielded by more electron shells. Cl
The further the outer shell is from the positive attraction of the nucleus, the harder it is to attract another electron to complete the outer shell. Br
This is why the reactivity of the halogens decreases going down group 7.