9701 · 27.1
Similarities and trends in the properties of the Group 2 metals, magnesium to barium, and their compounds
Group 2 elements, the alkaline earth metals, show predictable changes in their properties as you go down the group. These trends, from reactivity to solubility, are all explained by the increasing size of the atoms and ions.
Need to know
What you need to know
- **Atomic Radius:** Increases down the group due to the addition of electron shells.
- **First Ionisation Energy:** Decreases down the group. The outermost electrons are further from the nucleus and experience increased shielding from inner shells, making them easier to remove despite the increasing nuclear charge.
- **Melting Point:** Generally decreases down the group, but the trend is not perfectly regular (Magnesium is an anomaly). This is because the metallic bonding gets weaker as the atomic size increases and the distance between the positive nuclei and the delocalised electrons increases.
- **Reactivity:** Increases down the group. The lower ionisation energy means it is easier for the atoms to lose their two valence electrons and form a 2+ ion.
Explanation
Group 2: Down the Group Trends
- A Level Group 2: solubility SO₄²⁻ ↓, OH⁻ ↑ down group. | Sim hint: BaSO₄ insoluble — barium meal.
- Thermal stability CO₃²⁻ and NO₃⁻ increases down group. | Sim hint: Decomposition temperature trend.
- Complex ion formation less central than transition metals. | Sim hint: Contrast with d-block chemistry.
- Link to lattice energy and ionic radius arguments. | Sim hint: Born–Haber style reasoning at A Level.