9701 · 10.1
Similarities and trends in the properties of the Group 2 metals, magnesium to barium, and their compounds
Group 2 metals show predictable trends down the group because their atoms get larger and lose electrons more easily. This affects everything from how they react with water to the properties of the compounds they form.
Need to know
What you need to know
- **Atomic Radius:** Increases down the group (more electron shells).
- **Shielding:** Increases down the group (more inner electrons).
- **Ionisation Energy:** Decreases down the group (weaker nuclear attraction for valence electrons).
- **Reactivity:** Increases down the group (easier to form M²⁺ ions).
Explanation
The Alkaline Earth Trendsetters
- Reactivity increases down Group 2. This is because ionisation becomes easier, a factor that outweighs changes in lattice and hydration enthalpies.
- The general equations are M + 2H₂O → M(OH)₂ + H₂ and M + 2HCl → MCl₂ + H₂. Observations, like fizzing rate, are more vigorous for barium than magnesium.
- Thermal stability of carbonates/nitrates increases down the group. The larger cation at the bottom of the group has a lower charge density and polarises the anion less.
- Solubility trends are crucial: hydroxides become more soluble down the group, while sulfates become less soluble. This makes BaSO₄ an insoluble salt.