Group 2 elements:  Redox eactions:

The Group 2 elements:

• These are also called the alkaline earth metals as their hydroxides are alkaline.

• Remember that the reactivity increases as you move down Group 2 (see ionisation energies)

Physical properties:

• All light metals.

• Compounds are white or colourless.

• They have reasonably high melting and boiling points.

Electronic configuration:

• All in the s block sub - shell and all have s² electrons.

Reactivity of Group 2 elements:

• Group 2 metals are reactive:

• These elements give away 2 electrons when they react.

• This means that what ever they react with must gain electrons.

• Gaining electrons is a reduction reaction:

Oxidation

            Is

            Loss of electrons

            Reduction

            Is

            Gain of electrons

• As the Group 2 elements cause the reduction of other compounds or elements we say it is a good Reducing agent.

• Reactivity increases as you go down the Group.  This means they lose their electrons more readily.

• This means as you go down Group 2, they become better Reducing agents

Reaction with oxygen

• Group 2 metals react vigorously with oxygen to give the oxide:

Metal              +          Oxygen      à           Metal oxide

• The reaction gives an ionic product. If you apply oxidation numbers, you can see what has been oxidised and reduced:

Reaction with water

• Group 2 metals react with water to give the hydroxide and hydrogen gas:

Metal              +          Water          à           Metal hydroxide         +          Hydrogen

• The reaction gives an ionic product. If you apply oxidation numbers, you can see what has been oxidised and reduced:

• Note that only one of the H from each water molecule has been reduced

Questions 1 - 2  P89

Group 2 compounds:  reactions

Group 2 oxides and hydroxides:

• These are bases as they neutralise acids to form salts and water:

1)  Group 2 oxides:

• These react with water to form metal hydroxide.

• These are soluble so dissolve in the water forming an alkali, pH10 - 12

2)  Group 2 hydroxides:

• As these are soluble, they dissolve in water forming alkaline solutions::

The solubility of the Group 2 hydroxides increases as you go down the Group. This means that as you go down Group 2 more hydroxide ions are formed (for the same amounts). This means that as you go down Group 2 they become more alkaline.

3)  Group 2 carbonates:

• The Group 2 carbonates decompose when heated, Thermal Decomposition:

            Is the breaking down of a chemical substance with heat into at least 2 chemical substances

As you go down Group 2, the carbonates become harder to decompose.

Properties of Group 2 elements and their compounds:

• Because of Periodicity we only have to learn the Chemistry for one of the elements in Group 2.

• All the elements in Group 2 will react in the same way (but with different vigour).

• As you go down Group 2: the elements become more reactive.

• As you go down Group 2: the carbonates decompose at higher temperatures.

• As you go down Group 2: the hydroxides become more soluble in water, making the solution more alkaline.

Reactions of calcium and its compounds (or any Group 2 element / compound)

Uses of Group 2 hydroxides:

1)  Calcium hydroxide

• Is used to reduce the acidity of soil:

2)  Magnesium hydroxide

• Is used in indigestion tablets / 'milk of magnesia' to neutralise excess stomach acid.

 Questions 1 - 2  P91  /  4, 9, 11, and 12  P97  /  4  P98