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.

Key Concepts

Lattice Energy

Lattice energy is the amount of energy released when gaseous ions combine to form an ionic solid. It is a measure of the strength of the forces between the ions in an ionic compound. Higher lattice energy indicates stronger ionic bonds, which typically correlates with smaller ionic radii and higher charges on the ions.

Ionic Radius

Ionic radius refers to the size of an ion in a crystal lattice. Cations (positively charged ions) are generally smaller than their neutral atoms due to the loss of electrons, which reduces electron-electron repulsion. Understanding ionic radii is crucial for predicting the behavior of ions in compounds and their relative sizes, especially when comparing different elements.

Trends in Group 2 Elements

In Group 2 elements, ionic radius increases down the group due to the addition of electron shells. This trend affects the lattice energies of their compounds, as larger ions typically lead to lower lattice energies. Recognizing these trends helps in predicting the properties of compounds formed by these elements, including their similarity to other ions, such as Zn²⁺.