Group 7 Halogens – Properties Reactions Colours | O Level

Prof. Faisal Mehmood Janjowa
December 4, 2025 6:01 am
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Group 7 Halogens – Properties, Reactions, Colours | O Level Chemistry 5070 | IGCSE Chemistry 0620 Group 7 Halogens – […]

Group 7 Halogens – Properties, Reactions, Colours | O Level Chemistry 5070 | IGCSE Chemistry 0620

Group 7 Halogens – Properties, Reactions, Colours

O Level Chemistry 5070 | IGCSE Chemistry 0620 | 100% Syllabus 2025–2027 | Past Papers Solved

Quick Mood Booster Before Starting Halogens!

    Group 7 Halogens (The Halogens): F₂, Cl₂, Br₂, I₂, At

    • 7 valence electrons → highly reactive non-metals

    • Exist as diatomic molecules (X₂)

    • Form 1– ions (halide ions)

Colours & Physical States (Most Asked Table)

Halogen	Formula	Colour	State at 25°C
Fluorine	F₂	Pale yellow		Gas
Chlorine	Cl₂	Greenish-yellow	Gas
Bromine	Br₂	Red-brown	Liquid
Iodine	I₂	Dark grey solid → purple vapour	Solid

Trends Down Group 7 (6–8 Marks Every Year)

Property	Trend	Reason
Melting / Boiling point	Increases	Larger molecules → stronger London forces
Reactivity	Decreases (F > Cl > Br > I)	Atomic radius increases → harder to gain an electron
Colour	Becomes darker	More energy of absorbed light decreases

Displacement Reactions – Memorise This!

More reactive halogen displaces less reactive one:

Cl₂ + 2KBr → 2KCl + Br₂ (red-brown colour)
Cl₂ + 2KI → 2KCl + I₂ (black solid / purple vapour)
Br₂ + 2KI → 2KBr + I₂ (brown → purple)
I₂ + KCl → no reaction

Memorise Whole Periodic Table (Groups 1–8) in One Song

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Group 7 Past Paper Questions Solved by Prof. Faisal

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