REVISION NOTES

IGCSE Edexcel Chemistry

2.2 Group 7 (Halogens) – Chlorine, Bromine and Iodine

2.2.1 Know the colours, physical states (at room temperature) and trends in physical properties of these elements

GROUP 7 ELEMENTS

  • They are known as halogens
  • Poisonous non-metals
  • Similar chemical properties because they have the same number of electrons in the outer shell
  • Halogens are diatomic, meaning they form molecules with two halogen atoms sharing electrons

Trends in physical properties

edexcel_igcse_chemistry_topic 11 tables_group 7 (halogens) chlorine, bromine, and iodine_001_halogens trends in physical properties

TREND 1:

Melting and boiling points increase down the group

  • Size of halogen molecules increases down the group
  • Increasing intermolecular forces
  • More energy is required to overcome the forces
edexcel_igcse_chemistry_topic 11_group 7 (halogens) chlorine, bromine, and iodine_001_halogens group 7 melting and boiling points graph

TREND 2

At room temperature, the physical state of halogens changes down the group

  • This is also due to the increasing intermolecular forces
edexcel_igcse_chemistry_topic 11_group 7 (halogens) chlorine, bromine, and iodine_002_ chlorine bromine and iodine state of matter diagram room temperature

TREND 3

Colours of halogens changes down the group

  • Becomes darker

2.2.2 Use knowledge of trends in Group 7 to predict the properties of other halogens

RECALL: (DOWN THE GROUP)

  • Melting and boiling points increase
  • Colour becomes darker
  • Physical state at room temperature starts from gas, to liquid, to solid

Halogens can also react with metals and non–metals to form compounds

  • Halogen + Metal
  • Halogen + Non–metal
  • This can be used to predict the properties of other halogens as they share similar chemical properties

REACTION 1 HALOGEN + METAL

 

Halogen + Metal → Metal halide (salt, ionic compound)

  • Metals lose electrons from the valence shell
  • The electron(s) is
    gained by the halogen, forming halide ions with 1– charge
  • E.g. sodium + chlorine → sodium chloride

2Na + Cl2 → 2NaCl

  • E.g. calcium + bromine → calcium bromide

Ca + Br2 → CaBr2

REACTION 2 HALOGEN + NON-MENTAL

 

Halogens + Non-metal → simple covalent compounds

  • Halogens are also non-metals
  • Non–metals tend to gain electron(s) to become more stable
  • When non–metals bond together, they share electrons and form covalent compounds (Topic 7: Covalent Bonding)

Halogens + Hydrogen → Hydrogen halide

  • E.g. chlorine + hydrogen → hydrogen chloride

Cl2 + H2 → 2HCl

2.2.3 Understand how displacement reactions involving halogens and halides provide evidence for the trend in reactivity in Group 7

HALOGEN DISPLACEMENT REACTION

  • A more reactive halogen can displace a
    less reactive halide     in an aqueous solution
    • E.g. Cl2 can displace Br– ions in a solution to become Cl–
  • Whether or not the reaction can happen tells us which halogen is more reactive

REACTIVITY OF HALOGENS

  • The reactivity decreases down the group
  • Only reactions with chlorine, bromine and iodine will be studied
  • Reactivity Cl > Br > I, which means:
    • Chlorine can displace bromide and iodide
    • Bromide can displace iodide
edexcel_igcse_chemistry_topic 11_group 7 (halogens) chlorine, bromine, and iodine_003_chlorine bromine iodine order of reactivity diagram

Chlorine with bromides & iodides

  • Chlorine will displace bromide or iodide ions in a solution:

Cl2 + 2KBr → 2KCl + Br2

Chlorine + Potassium bromide → potassium chloride + Bromine

Cl2 + 2KI → 2KCl + I2

Chlorine + Potassium iodide→ potassium chloride + Iodine

Bromine with iodides

  • Bromine will displace iodide ions in a solution:

Br2 + 2KI → 2KBr + I2

Bromine + Potassium iodide → potassium bromide + Iodine

edexcel_igcse_chemistry_topic 11 tables_group 7 (halogens) chlorine, bromine, and iodine_002_halogens displacement reactions

2.2.4C Explain the trend in reactivity in Group 7 in terms of electronic configurations

RECALL

  • The reactivity of group 7 decreases down the group

WHEN HALOGENS REACT

  • Halogens have 7 electrons in the outer shell
  • When halogens react, they only need to gain one electron
  • As a result, it forms an anion with 1– charge

EXPLANATION OF TREND IN REACTIVITY

  • Reactivity of halogen depends on how easily the electron is gained
edexcel_igcse_chemistry_topic 11_group 7 (halogens) chlorine, bromine, and iodine_004_ chlorine bromine and iodine electronic configuration electron shells diagram
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Next

1.1 State of Matter

1.2 Elements, Compounds and Mixtures

1.3 Atomic Structure

1.4 The Periodic Table

1.5 Chemical Formulae, Equations and Calculations

1.6 Ionic Bonding

1.7 Covalent Bonding

1.8 Metallic Bonding

1.9 Electrolysis

2.1 Group 1 (Alkali Metals) – Lithium, Sodium and Potassium

2.2 Group 7 (Halogens) – Chlorine, Bromine and Iodine

2.3 Gases in the Atmosphere

2.4 Reactivity Series

2.5 Extraction and Uses of Metals

2.6 Acids, Alkalis and Titrations

2.7 Acids, Bases and Salt Preparations

2.8 Chemical Tests

3.1 Energetics

3.2 Rates of Reaction

3.3 Reversible Reactions and Equilibria

4.1 Introduction

4.2 Crude Oil

4.3 Alkanes

4.4 Alkenes

4.5 Alcohols

4.6 Carboxylic Acids

4.7 Esters

4.8 Synthetic Polymers

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