The Periodic Table: Group 7

Group 7 of the Periodic Table, better known as the Halogens, includes fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At).
Halogens have seven electrons in their outer shell. This means they are very reactive as they strive to gain that extra electron to achieve a stable full outer shell.
The reactivity of halogens decreases as you move down the group. Fluorine is the most reactive halogen, while astatine, usually the last halogen listed in textbooks, is the least reactive.
Halogens are highly reactive non-metals. They can form salts with metals, and they can also form molecular compounds with other non-metals.
The physical properties of halogens change down the group. Fluorine and chlorine are gases at room temperature, bromine is a liquid, and iodine and astatine are solids.
The density, boiling points and melting points of the halogens increase on moving down the group.
Halogens go from having very high electronegativities and electron affinities at the top of the group to much lower ones at the bottom of the group.
Halogens can exhibit multiple oxidation states, although they most commonly exhibit an oxidation state of -1 when forming ions.
They form diatomic molecules (meaning two atoms bond to form a molecule) in their natural state.
Fluorine is a pale yellow gas, chlorine is a green-yellow gas, bromine is a red-brown liquid, and iodine is a grey solid which produces a purple vapour when heated.
Here are a few examples of real-world applications of halogens: chlorine is used in water treatment to kill bacteria; iodine is used as an antiseptic; and fluorine is added to toothpaste to prevent tooth decay.

Remember, this information about Group 7 halogens can support learners’ knowledge of reactivity in other groups, patterns within the Periodic Table, and how these elements interact with their environment.