Similarities & Trends in the Properties of the Group 2 Metals, Magnesium to Barium, & Their Compounds (Cambridge (CIE) A Level Chemistry): Flashcards

Going down the group, the metal cations become larger and have a lower charge density. This reduces their polarising effect on the carbonate or nitrate anion, so more heat is required to decompose the compound.

False.

The solubility of Group 2 sulfates decreases going down the group. The enthalpy of solution becomes more endothermic because the lattice enthalpy decreases more slowly than the enthalpy of hydration.

The standard enthalpy of solution (ΔH_sol^o) is the energy absorbed or released when one mole of an ionic solid dissolves in sufficient water to form a dilute solution under standard conditions. It can be exothermic or endothermic.

ΔH_sol^o = ΔH_hyd^o − ΔH_latt^o

The enthalpy of solution reflects the balance between the energy released on hydration of gaseous ions and the energy needed to overcome the lattice.

Going down Group 2, the charge density of the metal cation decreases and its polarising power on neighbouring anions decreases.

True.

For hydroxides, the lattice enthalpy decreases faster than the enthalpy of hydration going down the group, making the enthalpy of solution more exothermic and the hydroxides more soluble.

Smaller cations have a greater charge density (same 2+ charge packed into a smaller volume). This produces a stronger electric field that distorts the electron cloud of the anion more, making the anion more polarised and easier to decompose thermally.

Going down the group, the cations become larger. The ion-dipole interactions between the cation and water molecules weaken, so less energy is released when the gaseous ions are hydrated.

Barium sulfate is insoluble in water, whereas barium hydroxide is soluble in water.