3.2.3.1 Trends in properties

The trends in electronegativity and boiling point of the halogens.

Students should be able to:

• explain the trend in electronegativity

• explain the trend in the boiling point of the elements in terms of their structure and bonding.

The trend in oxidising ability of the halogens down the group, including displacement reactions of halide ions in aqueous solution.

The trend in reducing ability of the halide ions, including the reactions of solid sodium halides with concentrated sulfuric acid.

The use of acidified silver nitrate solution to identify and distinguish between halide ions.

The trend in solubility of the silver halides in ammonia.

Students should be able to explain why:

• silver nitrate solution is used to identify halide ions

• the silver nitrate solution is acidified

• ammonia solution is added.

3.2.3.2 Uses of chlorine and chlorate(I)

The reaction of chlorine with water to form chloride ions and chlorate(I) ions.

The reaction of chlorine with water to form chloride ions and oxygen.

Appreciate that society assesses the advantages and disadvantages when deciding if chemicals should be added to water supplies.

The use of chlorine in water treatment.

Appreciate that the benefits to health of water treatment by chlorine outweigh its toxic effects.

The reaction of chlorine with cold, dilute, aqueous NaOH and uses of the solution formed.

Required practical 4

Carry out simple test-tube reactions to identify:

• cations – Group 2, NH4⁺