Consider the lattice energies of the following Group 2A compounds: BeH₂, 3205 kJ/mol; MgH₂, 2791 kJ/mol; CaH₂, 2410 kJ/mol; SrH₂, 2250 kJ/mol; BaH₂, 2121 kJ/mol. (d) The lattice energy of ZnH₂ is 2870 kJ/mol. Considering the trend in lattice enthalpies in the Group 2 compounds, predict which Group 2 element is most similar in ionic radius to the Zn²⁺ ion.

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1. Identify the trend in lattice energies for the Group 2A hydrides: BeH2, MgH2, CaH2, SrH2, and BaH2. Notice that the lattice energy decreases as you move down the group.
2. Understand that lattice energy is influenced by the charge and size of the ions. For ions with the same charge, smaller ions typically result in higher lattice energies due to stronger electrostatic attractions.
3. Compare the lattice energy of ZnH2 (2870 kJ/mol) with those of the Group 2A hydrides. ZnH2 has a lattice energy between that of MgH2 (2791 kJ/mol) and BeH2 (3205 kJ/mol).
4. Since the lattice energy of ZnH2 is closer to that of MgH2, it suggests that the ionic radius of Zn2+ is more similar to that of Mg2+ than to the other Group 2A ions.
5. Conclude that, based on the comparison of lattice energies, the Group 2 element with an ionic radius most similar to Zn2+ is magnesium (Mg).