Group 2 - Alkaline metals

Group 2 trends down the group - Reactivity

• Reactivity increases

• Atomic radius increases

• Shielding increases

• Nuclear attraction on outer electron decreases

• Ionisation energy decreases

Reactivity of Group 2 elements with oxygen

Observation:

• Bright white light

• White solid formed

Mg(s) + ½ O₂(g) → MgO(s)

Reactions of Group 2 elements with water

Metal(s) + Water(l) → Metal Hydroxide(aq) + Hydrogen(g)

Observation:

• Metal dissolves

• Fizzing

Solubility of Group 2 Hydroxides and pH

• Mg(OH)₂ - very sparingly soluble - pH:8-9

• Ca(OH)₂ - sparingly soluble- pH:10-11

• Sr(OH)₂ - slightly soluble - pH:11-12

• Ba(OH)₂ - soluble - pH:13-14

Reactions of Group 2 elements with dilute acids

Metal(s) + Acid(aq) → Salt(s) + Hydrogen(g)

Reaction of Group 2 compounds with acids

Base + Acid → Salt + Water

Uses of Group 2 elements and Compounds: Mg(OH)₂

Use:

• Neutralises excess stomach acid (HCl)

• Medicine

• Antacids

Equation:

Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O

Uses of Group 2 elements and Compounds: Ca(OH)₂

Use:

• Neutralises acidic soils (H2SO4)

• Agriculture

Equation:

Ca(OH)₂ + H₂SO4 → CaSO₄ + 2H₂O

Uses of Group 2 elements and Compounds: CaCO₃

Use:

• Limestone, Chalk or Marble

• Thermal decomposition gives CaO which is used to make cement

Equation:

CaCO₃ → CaO + CO₂