AQA GCSE FOUNDATION Chemistry: Group 7 - The Halogens

AQA GCSE Foundation Chemistry: Group 7 - The Halogens

Introduction

Group 7 of the periodic table contains the halogens. Halogens are very reactive non-metals, and they all have seven electrons in their outer shell. This means they need to gain one electron to achieve a stable electron configuration.

Reactivity patterns

• Reactivity decreases down the group: As you go down Group 7, the atoms get larger. This means the outer electron is further from the nucleus and is less attracted to it. This makes it easier for the atom to gain an electron, meaning the elements become less reactive.

• Displacement reactions: A more reactive halogen can displace a less reactive halogen from its salt solution. This means that if you add chlorine to a solution of potassium bromide, the chlorine will displace the bromine, forming potassium chloride and bromine.

Examples of halogens

• Fluorine (F): The most reactive halogen, used in toothpaste and non-stick cookware.
• Chlorine (Cl): A greenish-yellow gas, used to purify water.
• Bromine (Br): A reddish-brown liquid, used in photography and medicines.
• Iodine (I): A dark grey solid, used in disinfectants and in the treatment of thyroid problems.

Displacement reactions

Displacement reactions are reactions where a more reactive element displaces a less reactive element from its compound. Here's how they work with halogens:

1. Reaction: When a halogen is added to a solution of a halide salt, the halogen will displace the halide ion if it is more reactive.

2. Example: Chlorine (Cl) is more reactive than bromine (Br). If chlorine gas is bubbled through a solution of potassium bromide (KBr), the following reaction will occur:

   Cl?(g) + 2KBr(aq) ? 2KCl(aq) + Br?(l)

   • Chlorine displaces bromine from the potassium bromide solution, forming potassium chloride and bromine.

3. Observations: You would see a change in color as the bromine is released from the solution.

Key points to remember

• Halogens are very reactive non-metals.
• Reactivity decreases down Group 7.
• More reactive halogens can displace less reactive halogens from their salts.
• Displacement reactions are a good way to test the relative reactivity of halogens.

Further exploration

• Research the uses and properties of different halogens.
• Investigate how halogens are used in everyday life.
• Design an experiment to test the relative reactivity of different halogens.