27 Group 2

27.1 Similarities and Trends in the Properties of Group 2 Metals (Magnesium to Barium) and their Compounds:

  1. Thermal Stability of Nitrates and Carbonates:
    1. Trend: The thermal stability of nitrates and carbonates of Group 2 metals decreases as you move down the group.
    2. The decrease in thermal stability is attributed to the increasing ionic radius of the metal ions down the group. Larger metal ions have a lower charge density, which leads to weaker electrostatic interactions with the anions in the compounds. As a result, it requires less energy to break the metal-anion bonds and decompose the compounds upon heating. Additionally, larger metal ions have a higher polarizing power, which causes greater distortion of the anions and further reduces the stability of the compounds.
  2. Solubility and Enthalpy Change of Solution (ΔH⦵sol) of Hydroxides and Sulfates:
    1. Solubility Trend of Hydroxides: The solubility of Group 2 metal hydroxides increases as you move down the group.
      1. The increase in solubility is due to the increase in ionic radius and the corresponding decrease in lattice energy. Larger metal ions have weaker attractive forces between cations and anions in the crystal lattice, making it easier for the hydroxide compounds to dissolve in water.
    2. Enthalpy Change of Solution Trend of Hydroxides: The enthalpy change of solution becomes more negative (more exothermic) as you move down the group.
      1. The more negative enthalpy change is a result of the increasing strength of the ion-dipole interactions between the metal cations and water molecules during the process of hydration. As the metal ions increase in size, they have a greater charge density and can form stronger attractions with the water molecules, leading to a more exothermic process of solvation.
    3. Solubility Trend of Sulfates: The solubility of Group 2 metal sulfates decreases as you move down the group.
      1. The decrease in solubility is primarily due to the increasing lattice energy of the sulfates as the metal ions become larger. Larger metal ions have stronger attractive forces between cations and anions, resulting in a more stable crystal lattice and lower solubility in water.
    4. Enthalpy Change of Solution Trend of Sulfates: The enthalpy change of solution becomes less negative (less exothermic) as you move down the group.
      1. The less negative enthalpy change is a consequence of the increasing endothermicity of the hydration process. Larger metal ions have a lower charge density and weaker interactions with water molecules, leading to a less exothermic process of solvation.