Unit Overview

Group 2 and Group 17

CIE A-Level Chemistry· 5 min read 📊 n/a

1. Unit at a glance

This unit builds on your core knowledge of periodicity to explore two core inorganic groups. We start with Group 2 (s-block alkaline earth metals), investigating how reactivity, solubility of compounds, and thermal stability change down the group. We then move to Group 17 (p-block halogens), covering trends in oxidizing power, displacement reactions, and characteristic tests for halide ions.

This unit contains two core sub-topics:

Group 2 properties and reactions

Covers physical trends, common reactions, and trends in solubility and thermal stability of Group 2 compounds

★★⏱ 15 min

Group 17 properties and reactions

Explores physical trends, reactivity, displacement reactions, and halide identification tests for Group 17

★★★⏱ 18 min

2. Common Pitfalls

Wrong move:

Confusing the solubility trend for Group 2 hydroxides and sulfates

Why:

Learners often reverse the two trends, leading to incorrect predictions in exam questions

Correct move:

Remember: Hydroxide solubility increases down Group 2, sulfate solubility decreases down Group 2

Wrong move:

Reversing halogen displacement reaction direction

Why:

Many learners incorrectly write that lower halogens displace higher halide ions from solution

Correct move:

Only a more reactive (higher up Group 17) halogen can displace a less reactive halide ion from its salt

3. Quick Reference Cheatsheet

Concept	Key Trend/Fact
Group 2 reactivity	Increases down the group: first ionisation energy decreases, electrons are lost more easily
Group 2 hydroxide solubility	Increases down the group: $M g (O H)_{2}$ sparingly soluble, $B a (O H)_{2}$ highly soluble
Group 2 sulfate solubility	Decreases down the group: $M g S O_{4}$ soluble, $B a S O_{4}$ completely insoluble
Group 17 reactivity	Decreases down the group: electronegativity decreases, harder to gain an outer electron
Halogen oxidizing power	Decreases down the group: order of strength: $C l_{2} > B r_{2} > I_{2}$
Halide ion test	Add dilute $H N O_{3}$ then $A g N O_{3}$ : AgCl (white), AgBr (cream), AgI (yellow)

What's Next

Begin your study of this unit with the first sub-topic on Group 2 properties and reactions. Work through both sub-topics to master all trends and reactions required for assessment, then move on to the next unit covering nitrogen and sulfur chemistry.