Chapter 8 - Reactivity Trends

Group 2 elements react by losing or sharing electrons. Reactivity increases down the group due to a decrease in first and second ionisation energies. This is due to: - Increasing atomic radius - Increasing electron shielding - Less attraction between the nucleus and the outer electrons. - Electrons are lost more easily.

A substance which reduces other things but are themselves oxidised. Vice versa for oxidising agents.

Metal + Oxygen → Metal Oxide

Metal + Water → Metal Hydroxide + Hydrogen

Metal Oxide + Water → Alkaline solution

Metal Hydroxide + Water → Precipitate OR Alkaline solution Group 2 hydroxides are only slightly soluble in water and much of the hydroxide product may form a precipitate instead of an alkaline solution.

The solubility of Group 2 hydroxides in water increases down the group. The solutions become more alkaline because they contain more OH- (aq) ions.

• Calcium hydroxide is used in agriculture to neutralise acid soils • Magnesium hydroxide and calcium carbonate are used as ‘antacids’ to neutralise acids that cause indigestion.

The boiling points of the halogens increase down the group. • The halogens exist as diatomic molecules (e.g. Cl2, Br2) • In the solid state, the halogens form simple molecular lattices, with weak London forces between the halogen molecules. • Down the group, the halogen molecules contain more electrons, increasing the strength of the London forces. • More energy is required to break the London forces, increasing the boiling point.

Halogens react by gaining or sharing an electron. Reactivity decreases down the halogen group: - Increased number of shells so increased atomic radius and shielding - The attraction between the nucleus and the outer electrons decreases - The attraction for an external electron decreases.

Aqueous solution - Pale green + cyclohexane - Pale green

Aqueous solution - Orange + cyclohexane - Orange

Aqueous solution - Brown + cyclohexane - Violet

Reactivity of halogens decreases down the group. • A solution of each halogen is mixed with solutions of the other halides • If a reaction takes place, the halogen (higher in the group) oxidises the halide ion, removing an electron from each halide ion.

…a yellow gas.

…a pale-green gas.

…a red-brown liquid.

…a dark-grey solid.