Group 2: Aka alkaline earth metals.
• Redox Reactions: They are the most common type of reaction of Group 2 elements. Each metal
atom is oxidised, losing two electrons to form a X2+ ion- the same electron configuration as noble
gas. Another species will gain these two electrons and be reduced.
• Reducing Agent: A reagent that reduces (adds electrons to) another species. Group 2 are reducing
agents.
• Redox Reactions with Oxygen: Group 2 reacted with oxygen forms metal oxide. General formula
is XO would be made of an X2+ and O2-
ions.
• 2Mg (s) + O2 (g) -> 2MgO (s). Magnesium is oxidised. Oxygen is reduced. So the total increase is +4
in oxidation number and total decrease is -4, which balances.
• Redox Reactions with Water:
– Group 2 reacted with water forms alkaline hydroxide and hydrogen gas.
– General formula is X (s) + 2H2O (l) -> X(OH)2 (aq) + H2 (g).
• Redox Reactions with Dilute Acids: Metal (s) + acid (aq) -> salt (aq) + hydrogen (g). Would see
bubbles and named metal dissolve.
• Reactivity: Magnesium and water react slowly but reactions get more vigorous and quicker rate
with metals further down groups- what would be observed.
• Reactivity increases down the group…
– Group 2 react to form +2 ions, so first and second ionisation energies.
– Atomic radius increases.
– More shells so more shielding.
– Nuclear attraction to electron decrease.
– So easier to remove outer electron because ionisation energy decreases.
– Also means Group 2 become stronger reducing agents down the group.
• Group 2 Compounds:
• Group 2 Oxides and Water: Group 2 oxides react with water, releasing hydroxide ions (OH-
),
forming alkaline solutions of metal hydroxide. CaO (s) + H2O -> Ca2+ (aq) + 2OH-
(aq).
• Solid Precipitate: Group 2 hydroxides are only slightly soluble in water. When solution becomes
more saturated, any further metal and hydroxide ions form a solid precipitate- Ca2+ (aq) + 2OH-
(aq) -> Ca(OH)2 (s). CaO (s) + H2O -> Ca(OH)2
• Solubility of Hydroxides: Solubility of hydroxides in water, increases down the group from Mg, so
resulting solutions contain more OH-
(aq) ions and are more alkaline (pH increases).
• Use in Agriculture: Calcium hydroxide, Ca(OH)2, added to neutralise acid in soil. Ca(OH)2 (s) + 2H+
(aq) -> Ca2+ (aq) + 2H2O (l). Excess will result in soils becoming too alkaline to sustain crop growth.
• Use in Medicine: Acid indigestion tablets- magnesium and calcium carbonates. ‘Milk of Magnesia’-
magnesium hydroxide. Acid in stomach HCl.
• CaCO3 (s) + 2HCl (aq) -> CaCl2 (aq) + H2O (l) + CO2 (g).
Mg(OH)2 (s) + 2HCl (aq) -> MgCl2 (aq) + 2H2O (l).
• If CaSO3 formed instead, means used H2SO3.
