Topic 4: Inorganic Chemistry and the Periodic Table
Topic 4A: The elements of Groups 1 and 2
1. understand reasons for the trend in ionisation energy down Group 2
Trends in Group 2
Ionisation energy decreases down group 2:
- As you go down the group, the elements gain an electron shell which increases shielding
- The valence electrons are also further away from the nucleus as nuclear radius increases
Therefore, the valence electron is easier to remove hence ionisation energy decreases
2. understand reasons for the trend in reactivity of the Group 2 elements
down the group
Reactivity increases down group 2:
- As you go down the group, the two valence electrons become easier to remove
This means they more readily lose their electrons hence are more reactive
3. know the reactions of the elements Mg to Ba in Group 2 with oxygen,
chlorine and water
Group 2 reactions
Group 2 elements
Reaction with oxygen
Group 2 metals burn in oxygen to form solid white oxides
2Mg(s) + O2(g) 2MgO(s) Burns with bright white flame
2Ca(s) + O2(g) 2CaO(s) Burns with red flame
Ba(s) + O2(g) BaO2(s) Burns with a pale green flame
Reaction with water
Group 2 metals react with oxygen to form metal hydroxide and hydrogen
Mg(s) + 2H2O(l) Mg(OH)2(aq) + H2(g) Reacts slowly
Mg(s) + H2O(g) MgO(s) + H2(g) If the water is steam, magnesium reacts faster
Ba(s) + 2H2O(l) Ba(OH)2(aq) + H2(g) Reacts fastest and the hydroxide is quite soluble
Reaction with chlorine
Group 2 metals all react with chlorine to form solid white chlorides
Mg(s) + Cl2(g) MgCl2(s)
4. know the reactions of the oxides of Group 2 elements with water and dilute
acid, and their hydroxides with dilute acid
Group 2 oxides
Reaction with water
Group 2 metal oxides react with water to form metal hydroxides which then dissolve in the
water. The OH- makes the solution very alkaline.
CaO(s) + H2O(l) Ca(OH)2(aq)
Beryllium is an exception – it doesn’t react with water and Be(OH)2 is insoluble. Magnesium
hydroxide also isn’t very soluble. The oxides form more strongly alkaline solutions as you go
down the group as the metal hydroxides become more soluble.
Reaction with dilute acid
Group 2 metal oxides are basic so when they react with acids, they neutralise them to form salts.
CaO(s) + 2HNO3(aq) Ca(NO3)2(aq) + H2O(l)
Topic 4A: The elements of Groups 1 and 2
1. understand reasons for the trend in ionisation energy down Group 2
Trends in Group 2
Ionisation energy decreases down group 2:
- As you go down the group, the elements gain an electron shell which increases shielding
- The valence electrons are also further away from the nucleus as nuclear radius increases
Therefore, the valence electron is easier to remove hence ionisation energy decreases
2. understand reasons for the trend in reactivity of the Group 2 elements
down the group
Reactivity increases down group 2:
- As you go down the group, the two valence electrons become easier to remove
This means they more readily lose their electrons hence are more reactive
3. know the reactions of the elements Mg to Ba in Group 2 with oxygen,
chlorine and water
Group 2 reactions
Group 2 elements
Reaction with oxygen
Group 2 metals burn in oxygen to form solid white oxides
2Mg(s) + O2(g) 2MgO(s) Burns with bright white flame
2Ca(s) + O2(g) 2CaO(s) Burns with red flame
Ba(s) + O2(g) BaO2(s) Burns with a pale green flame
Reaction with water
Group 2 metals react with oxygen to form metal hydroxide and hydrogen
Mg(s) + 2H2O(l) Mg(OH)2(aq) + H2(g) Reacts slowly
Mg(s) + H2O(g) MgO(s) + H2(g) If the water is steam, magnesium reacts faster
Ba(s) + 2H2O(l) Ba(OH)2(aq) + H2(g) Reacts fastest and the hydroxide is quite soluble
Reaction with chlorine
Group 2 metals all react with chlorine to form solid white chlorides
Mg(s) + Cl2(g) MgCl2(s)
4. know the reactions of the oxides of Group 2 elements with water and dilute
acid, and their hydroxides with dilute acid
Group 2 oxides
Reaction with water
Group 2 metal oxides react with water to form metal hydroxides which then dissolve in the
water. The OH- makes the solution very alkaline.
CaO(s) + H2O(l) Ca(OH)2(aq)
Beryllium is an exception – it doesn’t react with water and Be(OH)2 is insoluble. Magnesium
hydroxide also isn’t very soluble. The oxides form more strongly alkaline solutions as you go
down the group as the metal hydroxides become more soluble.
Reaction with dilute acid
Group 2 metal oxides are basic so when they react with acids, they neutralise them to form salts.
CaO(s) + 2HNO3(aq) Ca(NO3)2(aq) + H2O(l)
