Group 7 (Halogens) (Edexcel GCSE Chemistry: Combined Science)

• The elements in group 7 are known as the halogens
  • These are fluorine, chlorine, bromine, iodine and astatine

• These elements are non-metals that are poisonous
• All halogens have similar reactions as they each have seven electrons in their outermost shell
• Halogens are diatomic, meaning they form molecules made of pairs of atoms sharing electrons (forming a single covalent bond between the two halogen atoms)

Trends in Physical Properties

• At room temperature, the halogens exist in different states and colours, with different characteristics

The Appearance, Characteristics and Colour in Solution of the Halogens

• The melting and boiling points of the halogens increase as you go down the group
• This is due to increasing intermolecular forces as the atoms become larger, so more energy is required to overcome these forces

This graph shows the melting and boiling points of the group 7 halogens 

• At room temperature (20 °C), the physical state of the halogens changes as you go down the group
  • Fluorine and chlorine are gases, bromine is a liquid and iodine is crumbly solid

• The colours of the halogens also change as you descend the group - they become darker

The physical states and colours of chlorine, bromine and iodine at room temperature 

• The test for chlorine makes use of litmus paper
• If chlorine gas is present, damp blue litmus paper will be bleached white
• It may turn red briefly before bleaching, as acids are produced when chlorine comes into contact with water
• Chlorine should always be handled in a fume cupboard due to its toxicity