Group 2, the Akaline Earth Metals
9.1 The Physical and chemical
9.1 The Physical and Chemical Properties of Group 2
- The Group 2 metals are also called the alkaline earth metals because properties of group 2
their oxides and hydroxides are alkaline.
- All have 2 electrons in an outer s orbital.
- All form 2- ions with an oxidation state of -2.
- The atomic radius gets bigger down the group because there are more energy levels of electrons
- Group 2 metals have high melting points due to their metallic structure. The melting point gets lower as
you go down the group because metallic bonding is lower down the group. The attraction of the nucleus
for the delocalised electrons decreases down the group because the size of the metal ions increases
down the group. The anomaly of Mg is due to a change in the way the atoms pack together.
- Going down the group 1st ionisation energy decreases. The atomic radius gets bigger down the group,
there is more shielding down the group. Attraction between the nucleus and outer shell electrons
decreases down the group. Therefore, they are more reactive down the group.
- Group 2 metals are all oxidised in their reactions. The more reactive they are, the better they are at
being oxidised meaning they are better at reducing other species, therefore their reducing power
increases down the group.
- General equation for group 2 metals with water is
o M(s) + 2H2O(l) à M(OH)2(aq) + H2(g)
- Magnesium reacts slowly with cold water but rapidly with steam to form an alkaline oxide and hydrogen.
Calcium reacts the same way but more vigorously, even with cold water. Strontium and barium react
even more vigorously
- When magnesium reacts with steam
o Mg(s) + H2O(g) à MgO(s) + H2(g)
- Group 2 hydroxides are all white solids and become more soluble as you go down the group.
o Mg(OH)2 is almost insoluble. It is used in indigestion remedies to neutralise stomach acid which
causes heartburn and indigestion.
o Calcium hydroxide (slaked lime) is used to treat acidic soil and to maintain the optimum pH for
the plant.
- Group 2 sulfates become less soluble as you go down the group.
o Barium sulfate is virtually insoluble, this means it can be taken by mouth to outline the gut in
medical X-rays. Even though barium is highly toxic it is safe to ingest BaSO4 to do because it is
so insoluble.
o The insolubility of barium sulfate is also used as a test for sulfate ions in a solution. Nitric or
hydrochloric acid is added to the solution, then barium chloride solution is added and is a sulfate
is present a white precipitate is formed. The acid removes carbonate ions which could give a
false positive.
- Magnesium is used in the extraction of titanium from TiCl4. It reduces TiCl4.
o TiCl4(l) + 2Mg(s) à2MgCl2(s) + Ti(s)
9.1 The Physical and chemical
9.1 The Physical and Chemical Properties of Group 2
- The Group 2 metals are also called the alkaline earth metals because properties of group 2
their oxides and hydroxides are alkaline.
- All have 2 electrons in an outer s orbital.
- All form 2- ions with an oxidation state of -2.
- The atomic radius gets bigger down the group because there are more energy levels of electrons
- Group 2 metals have high melting points due to their metallic structure. The melting point gets lower as
you go down the group because metallic bonding is lower down the group. The attraction of the nucleus
for the delocalised electrons decreases down the group because the size of the metal ions increases
down the group. The anomaly of Mg is due to a change in the way the atoms pack together.
- Going down the group 1st ionisation energy decreases. The atomic radius gets bigger down the group,
there is more shielding down the group. Attraction between the nucleus and outer shell electrons
decreases down the group. Therefore, they are more reactive down the group.
- Group 2 metals are all oxidised in their reactions. The more reactive they are, the better they are at
being oxidised meaning they are better at reducing other species, therefore their reducing power
increases down the group.
- General equation for group 2 metals with water is
o M(s) + 2H2O(l) à M(OH)2(aq) + H2(g)
- Magnesium reacts slowly with cold water but rapidly with steam to form an alkaline oxide and hydrogen.
Calcium reacts the same way but more vigorously, even with cold water. Strontium and barium react
even more vigorously
- When magnesium reacts with steam
o Mg(s) + H2O(g) à MgO(s) + H2(g)
- Group 2 hydroxides are all white solids and become more soluble as you go down the group.
o Mg(OH)2 is almost insoluble. It is used in indigestion remedies to neutralise stomach acid which
causes heartburn and indigestion.
o Calcium hydroxide (slaked lime) is used to treat acidic soil and to maintain the optimum pH for
the plant.
- Group 2 sulfates become less soluble as you go down the group.
o Barium sulfate is virtually insoluble, this means it can be taken by mouth to outline the gut in
medical X-rays. Even though barium is highly toxic it is safe to ingest BaSO4 to do because it is
so insoluble.
o The insolubility of barium sulfate is also used as a test for sulfate ions in a solution. Nitric or
hydrochloric acid is added to the solution, then barium chloride solution is added and is a sulfate
is present a white precipitate is formed. The acid removes carbonate ions which could give a
false positive.
- Magnesium is used in the extraction of titanium from TiCl4. It reduces TiCl4.
o TiCl4(l) + 2Mg(s) à2MgCl2(s) + Ti(s)
