3.1.4—Group trends
- Syllabus
- First assessment 2025
- Objective
- 3.1.4
- Level
- SL
Group Trends and Reactions
Group 1 becomes more metallic down the group, while Group 17 becomes less non-metallic down the group. These trends help predict displacement and reaction outcomes.
Use the reactivity order to decide whether a Group 1 metal reacts with water or whether a halogen displaces a halide ion, then write and explain the observation or equation.
Chlorine displaces bromide because Cl₂ is the stronger oxidizing agent: Cl₂ + 2Br⁻ → 2Cl⁻ + Br₂; bromine cannot reverse that reaction. For Group 1 with water, use the downward decrease in ionization energy to explain faster electron loss, then balance metal + water → hydroxide + H₂.
| Comparison | Observable evidence | Explanation check |
|---|---|---|
| Group 1 metal + water, moving down the group | hydrogen effervescence and metal motion become more vigorous; the solution formed is alkaline | outer electron is farther and more shielded, so electron loss becomes easier |
| Halogen + halide solution | a displacement is supported by formation of the less reactive halogen; observed colour must be interpreted for the stated aqueous/organic phase | the stronger oxidizing halogen gains electrons and oxidizes the halide |
Use observations as evidence, not as a substitute for a balanced equation. Detailed experimental procedure is outside this card.
Applying Group Reactivity
Assessment in practice
Representative question
Question 1
[Maximum number: 2]
Deduce the equation, and the colour change observed, for the reaction of dilute bromine water with aqueous iodide solution.
Equation:
Colour change:
Equation: Br2(aq)+2I−(aq)→2Br−(aq)+I2(aq)
Colour change: yellow/orange AND to red/brown
Marking guidance:
Accept that color is becoming darker-
darker orange etc, but do not accept
purple.
Accept correct equation that includes a
cation.
The Periodic Table Summary
Retrieve the route: locate an element from configuration, explain periodic and group trends, write oxide/reaction and oxidation-state answers, then connect incomplete d-sublevels to transition properties, ion configurations, and colours.
Check that every trend explanation names its particle-level cause, every equation is balanced, every oxidation state is a formal charge convention, and every transition colour uses absorbed/observed complementarity.