Reactivity of Halogens in Group 7

Key Objectives

Understand how the reactivity of halogens changes down Group 7.
Explain how a more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt.

Elements in Group 7 are known as halogens.
Halogens react with metals by gaining one electron to achieve a full outer energy level.
- Example: Fluorine reacting with lithium – the fluorine atom gains one electron from the lithium atom.

Fluorine is the most reactive element in Group 7.
Reactivity decreases as you move down the group.
Key points to learn:
- Fluorine is at the top and is most reactive.
- Chlorine is less reactive than fluorine.

Comparison between Fluorine and Chlorine:
- Chlorine gains electrons less easily than fluorine.
- Reasons for decreased reactivity in chlorine:
  1. Distance: Greater distance between the outer energy level and the nucleus in chlorine compared to fluorine.
  2. Shielding: More electrons in internal energy levels in chlorine, leading to greater shielding and less attraction to the nucleus.
Increased distance and shielding lower the attraction of outer electrons to the nucleus, making chlorine less reactive.

A more reactive halogen displaces a less reactive halogen in an aqueous solution of its salt.

Sodium Bromide and Fluorine
- Sodium bromide is in an aqueous solution.
- Fluorine is more reactive than bromine, so it displaces bromine.
- Result: A displacement reaction occurs.
Potassium Iodide and Chlorine
- Chlorine is more reactive than iodine.
- Chlorine displaces iodine.
- Products: Potassium chloride and iodine.
Lithium Chloride and Bromine
- Bromine is less reactive than chlorine.
- No displacement occurs as bromine cannot displace chlorine.
- Result: No reaction.

Revise with practice questions available in the revision workbook (link provided in the video).