Group VII: Colours, States & Sublimation
Past Paper Mastery · 15 Questions · 31 Total Marks
🧪 Examiner's Brief
Halogen colour and state questions appear in every paper. The marks are easy to lose — a single wrong descriptor ('yellow' instead of 'pale yellow-green') costs you the mark. Precision is everything.
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Section A
Colours & States
5 Qs · 10 marks
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Section B
Trends
5 Qs · 12 marks
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Section C
Sublimation
5 Qs · 10 marks
State the colour and physical state of chlorine (Cl₂) at room temperature and pressure (r.t.p.).
Think about what you would see if you opened a jar of chlorine gas in the lab.
State the colour and physical state of bromine (Br₂) at room temperature and pressure (r.t.p.).
Bromine is the only non-metal that is a liquid at room temperature.
State the colour and physical state of iodine (I₂) at room temperature and pressure (r.t.p.).
Iodine is the heaviest halogen studied at IGCSE and exists as a shiny solid.
Complete the table below for the halogens at r.t.p.: | Halogen | Colour | Physical State | |---------|--------|----------------| | Cl₂ | ? | ? | | Br₂ | ? | ? | | I₂ | ? | ? |
Go down the group: gas → liquid → solid. Colours deepen.
Which halogen is a liquid at room temperature and pressure?
Only ONE halogen in Group VII exists as a liquid at r.t.p.
Describe the trend in density of the halogens as you go down Group VII from chlorine to iodine.
Bigger atoms = bigger molecules = heavier = denser.
Describe the trend in physical state of the halogens as you go down Group VII from fluorine to iodine at r.t.p.
Fluorine and chlorine are gases. Bromine is a liquid. Iodine is a solid.
Explain why the boiling points of the halogens increase going down Group VII. [Supplement]
Think about intermolecular forces — van der Waals forces — and how atomic size affects them.
Describe the trend in reactivity of the halogens as you go down Group VII.
Which halogen is the most reactive — fluorine or iodine?
The colour of the halogens becomes darker going down the group. Arrange Cl₂, Br₂, and I₂ in order from lightest to darkest colour.
Compare pale yellow-green → red-brown → grey-black.
What is observed when solid iodine is gently heated in a test tube?
Iodine is unusual — it goes directly from solid to vapour without becoming a liquid first.
What is the name of the process in which a solid turns directly into a gas without passing through the liquid state?
This is a specific change of state with its own name.
A student heats iodine crystals and observes the gas produced. State the colour of the gas and name the process occurring.
Two-part answer needed: the colour AND the process name.
When iodine vapour cools on a cold surface, what change of state occurs and what would you observe?
The reverse of sublimation also has a name.
A student places a small amount of solid iodine at the bottom of a sealed glass tube. She gently warms the tube and then allows it to cool. Describe the full sequence of observations the student would make from start to finish.
Think in stages: (1) before heating, (2) during heating, (3) after cooling.
The Three Laws of Halogen Memory
Cl₂
Pale YELLOW-GREEN gas
Br₂
RED-BROWN liquid
I₂ vapour
PURPLE gas (not the solid!)
Cambridge IGCSE Chemistry · Syllabus 0620 · Section 8.3.1
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