Topic 9 - Group 7 

Atomic and physical properties . . .Discusses trends in atomic radius, electronegativity, electron affinity and melting and boiling points of the Group 7 elements. It also looks at the bond strengths of halogen-halogen bonds and of hydrogen-halogen bonds.

Halogens as oxidising agents . . .Describes and explains the trend in oxidising ability of the Group 7 elements based on the reactions between one halogen and the ions of another one - for example, between Cl2 and I- ions from salts like KI.

The acidity of the hydrogen halides . . .Discusses the acidity of the hydrogen halides (like hydrogen chloride), and explains why HF is a weak acid.

Halide ions as reducing agents . . .Describes and explains the trend in reducing ability of the halide ions based on their reactions with concentrated sulphuric acid.

Testing for halide ions . . .Describes and explains the tests for halide ions using silver nitrate solution followed by ammonia solution.

The manufacture of chlorine . . .Describes the manufacture of chlorine by the electrolysis of sodium chloride solution using a diaphragm cell and a membrane cell.

The Halogens are typical non-metals and form the 7th Group in the Periodic Table. 'Halogens' means 'salt formers' and the most common compound is sodium chloride which is found from natural evaporation as huge deposits of 'rock salt' or the even more abundant 'sea salt' in the seas and oceans.

  • They are typical non-metals with relatively low melting points and boiling points.

  • The melting points and boiling increase steadily down the group (so the change in state at room temperature from gas ==> liquid ==> solid), this is because the weak electrical intermolecular attractive forces increase with increasing size of atom or molecule.

  • They are all coloured non-metallic elements and the colour gets darker down the group.

  • They are all poor conductors of heat and electricity - typical of non-metals.

  • When solid they are brittle and crumbly e.g. iodine.

  • The size of the atom gets bigger as more inner electron shells are filled going down from one period to another.

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