What Are Group 7 Elements?

Group 7 elements are known as the halogens. These elements are found in the seventh column of the periodic table.

Examples of Group 7 elements include:

• Fluorine (F)
• Chlorine (Cl)
• Bromine (Br)
• Iodine (I)

Halogens are reactive non-metals that readily form salts when they react with metals.

The word halogen means “salt-former.”

Electronic Structure of Halogens

All Group 7 elements have seven electrons in their outer shell.

Example electron configurations:

• Fluorine → 2,7
• Chlorine → 2,8,7
• Bromine → 2,8,18,7

Because they only need one more electron to achieve a full outer shell, halogens gain electrons easily during chemical reactions.

This forms negative ions with a –1 charge.

Example:

Cl + e⁻ → Cl⁻

Physical Properties of Halogens

Halogens show interesting changes in physical properties as you move down the group.

States of Matter

At room temperature:

• Fluorine → Pale yellow gas
• Chlorine → Green gas
• Bromine → Reddish-brown liquid
• Iodine → Dark grey solid

This shows that the state of matter changes down the group.

Melting and Boiling Points

The melting and boiling points increase down the group.

This happens because larger atoms have stronger intermolecular forces.

Colour Changes

The colour of halogens becomes darker down the group.

Examples:

• Fluorine → Pale yellow
• Chlorine → Green
• Bromine → Red-brown
• Iodine → Dark purple / grey

Chemical Properties of Halogens

Halogens are very reactive non-metals.

However, their reactivity decreases down the group.

Fluorine is the most reactive halogen, while iodine is less reactive.

Reaction with Metals

Halogens react with metals to form ionic compounds called salts.

Example:

2Na + Cl₂ → 2NaCl

This reaction produces sodium chloride.

Reaction with Hydrogen

Halogens also react with hydrogen to form hydrogen halides.

Example:

H₂ + Cl₂ → 2HCl

Hydrogen chloride gas dissolves in water to form hydrochloric acid.

Displacement Reactions of Halogens

A more reactive halogen can displace a less reactive halogen from its compound.

Example:

Cl₂ + 2KBr → 2KCl + Br₂

In this reaction:

• Chlorine is more reactive than bromine
• Chlorine displaces bromine from potassium bromide

These reactions help identify the relative reactivity of halogens.

Uses of Halogens

Halogens are widely used in industry and everyday life.

Examples include:

• Chlorine used to disinfect drinking water
• Fluorine compounds used in toothpaste
• Iodine used as an antiseptic
• Bromine compounds used in flame retardants

These elements are important in medicine, sanitation, and chemical manufacturing.

Exam Tip (5070)

Students are often asked to:

• Describe physical properties of halogens
• Explain reactivity trends down Group 7
• Predict outcomes of halogen displacement reactions

Example exam question:

Why does reactivity decrease down Group 7?

Answer:

Reactivity decreases because atoms become larger and the nucleus attracts the incoming electron less strongly.

Practice Question

Which halogen is more reactive: chlorine or iodine?

Answer

Chlorine is more reactive than iodine.

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