Group 7 (Oxford AQA IGCSE Combined Science Double Award): Revision Note

Reactions of the Halogens

• The elements in Group 7 are known as the halogens

• The elements are:

  • Fluorine

  • Chlorine

  • Bromine

  • Iodine

  • Astatine

• Group 7 elements:

  • Are non-metals that are poisonous

  • Are diatomic

    • This means that they form molecules made of two atoms

    • The halogen atoms share electrons in a single covalent bond between them

    • These molecules are written as as F₂, Cl₂, etc.

• React with metals to form ionic compounds

  • The halogens form halide ions with a charge of -1

• All halogens have similar reactions as they each have seven electrons in their outermost shell

The electron structure of Group 7 elements

Trends in Group 7

• There are clear trends in reactivity, melting / boiling point and colour going down Group 7

• Moving down Group 7:

  • The reactivity of the halogens decreases

    • This pattern in the reactivity of the halogens can be observed by their displacement reactions

  • The melting / boiling point of the halogens increase

  • The colour of the halogens gets darker

Melting and boiling points down Group 7

• The melting / boiling points increase going down Group 7 because:

  • The atoms become larger

  • This means that there is an increase in intermolecular forces

  • So, more energy is required to overcome the increased intermolecular forces

  • This means that the melting / boiling point is higher

The melting and boiling points of the halogens

• The melting / boiling points affect the physical state of the halogens

• This is seen as a trend going down Group 7

  • At room temperature (20 °C), the physical states of the halogens are:

    • Fluorine and chlorine are gases

    • Bromine is a liquid

    • Iodine is crumbly solid

Colour down Group 7

• The colours of the halogens become darker going down Group 7

The colours of the halogens