8.3 Group VII Properties

2026 Syllabus Objectives

Core: Describe the Group VII halogens, chlorine, bromine and iodine, as diatomic non-metals with general trends down the group, limited to:
- (a) increasing density
- (b) decreasing reactivity
Core: State the appearance of the halogens at r.t.p. as:
- (a) chlorine, a pale yellow-green gas
- (b) bromine, a red-brown liquid
- (c) iodine, a grey-black solid
Core: Describe and explain the displacement reactions of halogens with other halide ions
Core: Predict the properties of other elements in Group VII, given information about the elements

Group VII – The Halogens

🔑 The halogens are elements found in Group VII of the Periodic Table and represent the most reactive group of non-metals. The main halogens studied at IGCSE level are chlorine, bromine, and iodine.

Common Properties of Halogens

All halogens share several characteristic properties:

They are all poisonous and have a similar strong smell
They are all non-metals
They all form diatomic molecules (e.g., $\text{Cl}_2$ , $\text{Br}_2$ , and $\text{I}_2$ )
They all have a valency of 1 and form compounds with similar formulae, e.g., hydrogen chloride ( $\text{HCl}$ ), hydrogen bromide ( $\text{HBr}$ ) and hydrogen iodide ( $\text{HI}$ )
Their compounds with hydrogen are usually strong acids when dissolved in water, e.g., hydrochloric acid ( $\text{HCl}$ ), hydrobromic acid ( $\text{HBr}$ ) and hydriodic acid ( $\text{HI}$ )
They each produce a series of compounds with other elements, known collectively as halides (e.g., chlorides, bromides and iodides)

🔑 Key Term: Halides are compounds formed between an element and a halogen, e.g., sodium iodide

Physical Properties and Trends

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Appearance at Room Temperature and Pressure (r.t.p.)

The three main halogens have distinct appearances at room temperature and pressure:

Halogen	State at r.t.p.	Colour
Chlorine ( $\text{Cl}_2$ )	Gas	Pale yellow-green (or pale-green)
Bromine ( $\text{Br}_2$ )	Liquid	Red-brown (or reddish-brown)
Iodine ( $\text{I}_2$ )	Solid	Grey-black (or greyish-black)

📌 Additional details:

Chlorine is a dense pale-green gas; smelly and poisonous; occurs as chlorides, especially sodium chloride in the sea; relative atomic mass 35.5
Bromine is a deep-red liquid with red-brown vapour; smelly and poisonous; occurs as bromides, especially magnesium bromide in the sea; relative atomic mass 80
Iodine is a grey solid with purple vapour; smelly and poisonous; occurs as iodides and iodates in some rocks and in seaweed; relative atomic mass 127

Trends Down Group VII

As you move down Group VII from fluorine to iodine, there are clear gradual changes in physical properties:

1. Physical State Changes:

The halogens change from gas → liquid → solid as you go down the group
This is because boiling points increase down the group

2. Density Increases:

There is an increase in density as you descend the group

3. Melting and Boiling Points Increase:

Halogen	Electronic Configuration	Melting Point (°C)	Boiling Point (°C)
Chlorine	2, 8, 7	-101	-35
Bromine	2, 8, 18, 7	-7	+59
Iodine	2, 8, 18, 18, 7	+114	+184

4. Colour Intensity Increases:

The intensity of colour increases from pale to dark going down the group
Following this trend, fluorine (at the top of the group) is a pale-yellow gas at room temperature

5. Reactivity Decreases:

In contrast with Group I, in Group VII reactivity decreases down the group
Fluorine is a dangerously reactive, pale-yellow gas at room temperature
The halogens become steadily less reactive as you go down the group

⚡ Important: The lowest element in Group VII is astatine, which is highly radioactive and rare. The actual properties of astatine remain largely unknown, but we can predict them based on the trends observed in the group.

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