Similarities and trends in the properties of the Group 2 metals, magnesium to barium, and their compounds

Summary

Group 2 metals, from magnesium to barium, show trends in reactivity, solubility, and thermal stability due to changes in atomic and ionic size, charge density, and bonding characteristics as you move down the group.

• Atomic Radius — the distance from the nucleus to the outermost electrons. Example: Increases down the group as electrons are added to new shells.
• Ionic Size — the size of an ion compared to its atom. Example: Increases down the group as the nuclear charge is less effective at holding electrons tightly.
• Melting Points — the temperature at which a solid becomes a liquid. Example: Decreases down the group due to weaker metallic bonding.
• Reactivity — how readily a substance undergoes a chemical reaction. Example: Increases down the group as ionization energy decreases.
• Thermal Stability — the ability of a compound to resist decomposition when heated. Example: Increases down the group as cations become larger and less polarizing.
• Solubility — the ability of a substance to dissolve in a solvent. Example: Hydroxides become more soluble, while sulfates become less soluble down the group.
• Enthalpy Change of Solution (ΔHsolꝋ) — the energy change when a solute dissolves in a solvent. Example: Becomes more exothermic for hydroxides and more endothermic for sulfates down the group.

Exam Tips

Key Definitions to Remember

• Atomic Radius: Distance from the nucleus to the outermost electrons.
• Ionic Size: Size of an ion compared to its atom.
• Melting Points: Temperature at which a solid becomes a liquid.
• Reactivity: How readily a substance undergoes a chemical reaction.
• Thermal Stability: Ability of a compound to resist decomposition when heated.
• Solubility: Ability of a substance to dissolve in a solvent.
• Enthalpy Change of Solution (ΔHsolꝋ): Energy change when a solute dissolves in a solvent.

Common Confusions

• Confusing the trend of solubility for hydroxides and sulfates.
• Misunderstanding why reactivity increases down the group.

Typical Exam Questions

• Why does reactivity increase down Group 2? Answer: Due to decreasing ionization energy as atomic radius and electron shielding increase.
• How does ionic size change down Group 2? Answer: Ionic size increases as cations become larger.
• What happens to the melting points of Group 2 metals down the group? Answer: Melting points decrease due to weaker metallic bonding.

What Examiners Usually Test

• Trends in reactivity and their explanations.
• Differences in solubility trends between hydroxides and sulfates.
• Understanding of enthalpy changes related to solution and hydration.