8.3.4 — Halogen Reactivity Exam
Cambridge IGCSE Chemistry (0620) · Group VII · 15 Questions · 31 marks total
The Trend
Describe the trend in reactivity down Group VII (the halogens). [2]
💡 Hint: Think about what happens to the number of electron shells as you move down the group.
Which halogen is the most reactive? [1]
Which is more reactive — chlorine (Cl₂) or bromine (Br₂)? [1]
Explain, in terms of atomic structure, why iodine is less reactive than chlorine. [3]
💡 Hint: Compare their atomic radii, number of shells, and electron shielding.
State what is observed when chlorine gas is bubbled through a solution of potassium iodide (KI). Write a word equation for the reaction. [2]
💡 Hint: A more reactive halogen displaces a less reactive one from its salt.
Comparing Groups
Contrast the trend in reactivity down Group VII with the trend in reactivity down Group I. [2]
💡 Hint: One group gets more reactive going down; the other gets less reactive.
Explain why the reactivity of Group I metals increases down the group, using atomic structure. [2]
Which statement correctly compares Groups I and VII? [1]
A student says: 'Both Group I and Group VII elements become more reactive as atomic radius increases.' Evaluate this statement and correct any errors. [3]
💡 Hint: Think about whether halogens LOSE or GAIN electrons — and what atomic radius does to each process.
State the type of reaction halogens undergo when they react with metals, and give an example using chlorine and sodium. [2]
Application & Prediction
Predict whether fluorine is more or less reactive than chlorine. Give a reason. [1]
Astatine (At) is a halogen below iodine. Predict two properties of astatine, giving reasons based on Group VII trends. [2]
💡 Hint: Think about what happens to reactivity and physical state as you go down Group VII.
Bromine water is added to a solution of potassium chloride (KCl). State and explain whether a reaction occurs. [2]
The table shows three halogens. Complete the displacement reactions by predicting which occur and which do not. [3] Halogen added → Salt solution: (a) Cl₂(aq) → NaBr(aq) (b) I₂(aq) → NaCl(aq) (c) Br₂(aq) → NaI(aq)
A student investigates halogen displacement reactions using three unknown halogens: X, Y, and Z. They observe: • X displaces Y from its salt solution. • Z does not displace X from its salt solution. • Y displaces Z from its salt solution. Arrange X, Y, and Z in order of decreasing reactivity. Identify which known halogens they could be. [4]
💡 Hint: Build a reactivity series step by step from each observation.
📋 Professor's Mark Scheme Summary
Group VII Reactivity Trend (Core)
Reactivity decreases down Group VII. Larger atomic radius → outer shell further from nucleus → more shielding → weaker attraction for incoming electron.
Contrast with Group I (Supplement)
Group I reactivity increases down the group (easier to lose outer electron). Group VII reactivity decreases (harder to gain an electron).
Displacement Rule (Application)
A more reactive halogen displaces a less reactive halogen from its salt solution. Cl₂ displaces Br⁻ and I⁻. Br₂ displaces I⁻ only. I₂ displaces none.
Reactivity Order
F₂ > Cl₂ > Br₂ > I₂ > At₂
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