Group 7 & Group 0 (Halogens & Noble Gases)

This lesson covers:

  1. The properties of the halogens (group 7 elements)
  2. Reactions of halogens with metals
  3. Displacement reactions among the halogens
  4. Properties of the noble gases (group 0 elements)

For questions involving halogen displacement reactions, you will often be asked about the colour changes that take place. 

The key information to remember is:

  • Halide salts (e.g. KCl, KBr, KI) are colourless
  • Bromine water is orange
  • Chlorine water is colourless
  • Iodine water is brown

This means that when you mix chlorine water, bromine water, or iodine water with a halide salt you may get a colour change.

This table summarises the colour changes. We've shown the examples using potassium halides (KCl, KBr, KI), but the same logic would apply to other halide salts.


Table showing colour changes in halogen displacement reactions with halide salts, including KCl, KBr, and KI.

Colours and physical states of the halogens at room temperature


solid / gas / liquid / green / yellow / grey


  1. Fluorine is a poisonous coloured gas and is the most reactive halogen
  2. Chlorine is a coloured gas.
  3. Bromine is a red-brown volatile which is also poisonous. 
  4. Iodine is a coloured solid with purple vapours. 
yellow
green
liquid
grey

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Which two of these properties are seen in group 7 elements?

They exist as single atoms

Their ions usually have a 1- charge

They can form covalent bonds with other non-metals

Reactivity increases down the group

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Do the melting and boiling points of the halogens increase or decrease as you go down the group?

Increase

Decrease

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Periodic table with Group 7 elements highlighted in blue.

Based on the reactivity of the halogens, which of these displacement reactions is possible?

2HCl + I2  ➔ 2HI + Cl2

2HF + Cl2  ➔ 2HCl + F2

2HBr + F2  ➔ 2HF + Br2

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Diagram showing a diatomic chlorine molecule with two chlorine atoms sharing electrons to form a covalent bond.

double / diatomic / covalent / ionic


The halogens exist as molecules, meaning each molecule consists of two atoms.


The two atoms are joined by a bond, which allows each atom to share an electron, giving each atom a full outer shell.

diatomic
covalent

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Are noble gases flammable?

Yes

No

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Why are the noble gases inert?

('inert' means chemically unreactive)

The atoms have a full outer shell of electrons

They form colourless gases

The atoms are non flammable

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