Group 2 Chemistry Notes

Group 2 Metals

1. Reactions with Oxygen

• Generally, Group 2 metals burn in oxygen to form a metal oxide.
• Beryllium (Be):
  • Coated in a thin layer of beryllium oxide (BeO), which inhibits the reaction.
  • Reacts only in powder form.
  • Equation: 2Be + O_2 \rightarrow 2BeO
• Magnesium (Mg):
  • Burns in oxygen with a bright white flame.
  • Equation: 2Mg + O_2 \rightarrow 2MgO
• Calcium (Ca):
  • Burns with a bright white flame, slightly red at the top.
  • Equation: 2Ca + O_2 \rightarrow 2CaO
• Strontium (Sr):
  • Reluctant to start burning but burns intensely with a white flame.
  • Equation: 2Sr + O_2 \rightarrow 2SrO
• Barium (Ba):
  • Burns in oxygen with a white flame.
  • Equation: 2Ba + O_2 \rightarrow 2BaO

2. Reactions with Water

• Reactivity trend down the group can be observed through reactions with water or steam.
• Beryllium (Be):
  • Reacts with steam only at very high temperatures.
  • Equation: Be + H2O \rightarrow BeO + H2
• Magnesium (Mg):
  • Very slight reaction with cold water.
  • Reaction stops due to the production of an insoluble coat of magnesium hydroxide (Mg(OH)2).
  • Equation: Mg + 2H2O \rightarrow Mg(OH)2 + H_2
  • Burns more readily in steam than cold water.
  • Equation: Mg + H2O \rightarrow MgO + H2
• Calcium (Ca), Strontium (Sr), Barium (Ba):
  • React in cold water to produce their respective hydroxide and hydrogen gas.
  • Reactions become increasingly vigorous down the group.
  • Example: Ca + 2H2O \rightarrow Ca(OH)2 + H_2
• Reactivity increases down Group 2, with barium reacting the fastest.

3. Reactions with Dilute Acids

• All Group 2 metals react with dilute hydrochloric acid (HCl) to produce a metal chloride and hydrogen gas.
  • Reactions become more vigorous down the group.
  • General equation: X + 2HCl \rightarrow XCl2 + H2 (where X is a Group 2 metal).
• Dilute sulfuric acid (H2SO4) reacts with Group 2 metals to produce a metal sulfate and hydrogen.
  • Reactions do not get more vigorous down the group due to the solubility of the sulfates produced.
  • General equation: X + H2SO4 \rightarrow XSO4 + H2 (where X is a Group 2 metal).

4. Group 2 Oxides - Reactions

• Reactions with Water:
  • Apart from beryllium oxide (BeO), all Group 2 oxides react with water to produce hydroxides.
  • General Equation: XO + H2O \rightarrow X(OH)2
• Reactions with Dilute Acids:
  • All Group 2 oxides react with dilute acids to produce a salt and water.
  • General Equations (where X is a Group 2 metal):
    • With Hydrochloric Acid: XO + 2HCl \rightarrow XCl2 + H2O
    • With Nitric Acid: XO + 2HNO3 \rightarrow X(NO3)2 + H2O
    • With Sulfuric Acid: XO + H2SO4 \rightarrow XSO4 + H2O

5. Group 2 Hydroxides - Reactions

• Reactions with Water:
  • Group 2 hydroxides do not react with water.
• Reactions with Dilute Acids:
  • Group 2 hydroxides react with dilute acids similarly to metal oxides, producing a salt and water.
  • The only difference is that two water molecules are produced.
  • Example: Sr(OH)2 + 2HCl \rightarrow SrCl2 + 2H_2O

6. Metal Carbonates - Reactions

• Reactions with Water:
  • Group 2 metal carbonates are insoluble and do not react with water.
• Reactions with Dilute Acids:
  • Group 2 carbonates react with dilute acids, producing a salt, water, and carbon dioxide.
  • General Equations (where X is a Group 2 metal):
    • With Hydrochloric Acid: XCO3 + 2HCl \rightarrow XCl2 + H2O + CO2
    • With Nitric Acid: XCO3 + 2HNO3 \rightarrow X(NO3)2 + H2O + CO2
    • With Sulfuric Acid: XCO3 + H2SO4 \rightarrow XSO4 + H2O + CO2

7. Thermal Decomposition

• Nitrates:
  • All Group 2 nitrates undergo thermal decomposition to produce a metal oxide, oxygen, and nitrogen dioxide.
  • General Equation: 2X(NO3)2 \rightarrow 2XO + 4NO2 + O2
  • Observations:
    • Nitrate and oxide are white solids.
    • Nitrogen dioxide is a brown gas.
• Carbonates:
  • All Group 2 carbonates undergo thermal decomposition to produce a metal oxide and carbon dioxide.
  • General Equation: XCO3 \rightarrow XO + CO2
  • Observations:
    • Carbonate and oxide are white solids.
    • Carbon dioxide is a colourless gas.
• Stability:
  • Both Group 2 carbonates and nitrates become more stable to heat as you go down the group.
  • Stronger heating is required for thermal decomposition further down the group.

8. Predicting Trends

• Reactivity generally increases down Group 2 based on the reactions of metals, oxides, hydroxides, and carbonates.
• Reason: Ionization energy decreases due to increasing atomic radius and the shielding effect of electrons.
  • Electrons are easier to remove further down the group, leading to increased reactivity.
• Solubility:
  • Solubility of Group 2 hydroxides increases down the group.
  • Solubility of Group 2 sulfates decreases down the group.

9. Uses of Group 2 Compounds

• Calcium Hydroxide (Ca(OH)2) and Calcium Carbonate (CaCO3):
  • Used in agriculture.
  • Calcium carbonate is powdered limestone.
  • Calcium hydroxide is formed when calcium oxide (CaO) is added to water.
  • Calcium oxide and calcium hydroxide are referred to as lime and slaked lime, respectively, and are alkaline.
• Soil Acidity Correction:
  • Calcium hydroxide is added to acidic soil to bring the pH to 6, which is optimal for crop growth.