Group 7- The Halogens

Introduction to The Halogens

Introduction to The Halogens

Halogens is the name given to the elements that make up group VII of the Periodic Table. The group is composed of five halogens:

  • fluorine
  • chlorine
  • bromine
  • iodine
  • astatine

You will only need to concentrate on four of these elements as astatine is so radioactive that it is unable to exist for more than a few microseconds before it decays.

All of these elements are found most commonly as Xions in the -1 oxidation state. They are known as halide ions.

Structure

Each atom within this group consists of seven valence electrons and so tend to make diatomic molecules. Therefore, they are simple molecular which contain intermolecular forces between molecules.

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Appearance and colour

The table below outlines the colour and appearance of each element.

Halogen In pure form: In non-polar solvents: In water:
Fluorine pale yellow gas reacts with solvents reacts with water
Chlorine pale green gas pale green solution pale green solution
Bromine dark red liquid orange solution orange solution
Iodine grey solid purple solution insoluble but forms brown solution if a lot of Kl is present

The halogens tend to be used in aqueous solution. Iodine is insoluble in water however it is soluble if iodide ions are present: the iodine reacts with iodide ions and forms triiodide ions. It is the triiodide ions that create the brown colouration.

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Melting and boiling points

Halogen Melting point (