# Group 2 and Group 17

> CIE A-Level Chemistry · CIE 9701
> Source: https://www.owlsprep.com/study/cie-9701-u10-overview/
> Weight: n/a

This unit explores the physical and chemical properties of alkaline earth metals (Group 2) and halogens (Group 17), building on periodicity fundamentals to explain key trends and common reactions.

**Prerequisites:** Basic periodic table structure and periodic trends; [Redox reactions and oxidation numbers](https://www.owlsprep.com/study/cie-9701-u05-redox-reactions/)

## Learning objectives

- Explain periodic trends in physical and chemical properties across Group 2 and Group 17
- Predict products of common reactions of Group 2 and Group 17 elements and their compounds
- Relate observed reactivity trends to atomic structure and electronic configuration
- Apply redox concepts to explain displacement reactions of halogens

## 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](https://www.owlsprep.com/study/cie-9701-u10-group-2-properties-and-reactions/) — Covers physical trends, common reactions, and trends in solubility and thermal stability of Group 2 compounds
- [Group 17 properties and reactions](https://www.owlsprep.com/study/cie-9701-u10-group-17-properties-and-reactions/) — Explores physical trends, reactivity, displacement reactions, and halide identification tests for Group 17

## Common pitfalls

- **Wrong:** Confusing the solubility trend for Group 2 hydroxides and sulfates
  - Why it fails: Learners often reverse the two trends, leading to incorrect predictions in exam questions
  - Correct: Remember: Hydroxide solubility increases down Group 2, sulfate solubility decreases down Group 2
- **Wrong:** Reversing halogen displacement reaction direction
  - Why it fails: Many learners incorrectly write that lower halogens displace higher halide ions from solution
  - Correct: Only a more reactive (higher up Group 17) halogen can displace a less reactive halide ion from its salt

## 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: $Mg(OH)_2$ sparingly soluble, $Ba(OH)_2$ highly soluble |
| Group 2 sulfate solubility | Decreases down the group: $MgSO_4$ soluble, $BaSO_4$ 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: $Cl_2 > Br_2 > I_2$ |
| Halide ion test | Add dilute $HNO_3$ then $AgNO_3$: 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.

- [Group 2 properties and reactions](https://www.owlsprep.com/study/cie-9701-u10-group-2-properties-and-reactions/)
- [Group 17 Properties and Reactions](https://www.owlsprep.com/study/cie-9701-u10-group-17-properties-and-reactions/)
- [Nitrogen and sulfur](https://www.owlsprep.com/study/cie-9701-u11-overview/)

---

From [OwlsPrep](https://www.owlsprep.com) — free study guides for A-Level, IB, AP and IGCSE, written against the official syllabus. Canonical page: https://www.owlsprep.com/study/cie-9701-u10-overview/