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

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Physical Properties in Group 7

  • 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

new-2-2-1-group-7-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

Melting & boiling points of the Halogens, IGCSE & GCSE Chemistry revision notes

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

States of the Halogens, IGCE & GCSE Chemistry revision notes

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

Examiner Tip

Exam questions on this topic occur often so make sure you know and can state the trends of the group 7 elements in detail.

Testing Chlorine

  • 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

Test for Chlorine, IGCSE & GCSE Chemistry revision notes

Diagram showing the test for chlorine gas

Examiner Tip

You should distinguish between properties of gases and tests for gases. Chlorine 'smells like swimming pools' is a characteristic, but not an acceptable means of identification. You can use blue, red or universal indicator paper to show the bleaching effect.

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Stewart

Author: Stewart

Expertise: Chemistry Lead

Stewart has been an enthusiastic GCSE, IGCSE, A Level and IB teacher for more than 30 years in the UK as well as overseas, and has also been an examiner for IB and A Level. As a long-standing Head of Science, Stewart brings a wealth of experience to creating Exam Questions and revision materials for Save My Exams. Stewart specialises in Chemistry, but has also taught Physics and Environmental Systems and Societies.