Consider the lattice energies of the following Group 2 A compounds: Be H2, 3205 kJ / mol ; MgH2,

step 1 In this problem, we have to compare how various elements would bond to hydrogen. And we're going

Consider the lattice energies of the following Group 2 A...

Consider the lattice energies of the following Group 2 $\mathrm{A}$ compounds: $\mathrm{Be} \mathrm{H}_{2}, 3205 \mathrm{kJ} / \mathrm{mol} ; \mathrm{MgH}_{2}, 2791 \mathrm{kJ} / \mathrm{mol}$ $\mathrm{CaH}_{2}, 2410 \mathrm{kJ} / \mathrm{mol} ; \mathrm{SrH}_{2}, 2250 \mathrm{kJ} / \mathrm{mol} ; \mathrm{BaH}_{2}, 2121 \mathrm{kJ} / \mathrm{mol}$ (a) What is the oxidation number of $\mathrm{H}$ in these compounds? (b) Assuming that all of these compounds have the same three-dimensional arrangement of ions in the solid, which of these compounds has the shortest cation-anion distance? (c) Consider BeH $_{2} .$ Does it require 3205 kJ of energy to break one mole of the solid into its ions, or does breaking up one mole of solid into its ions release 3205 $\mathrm{kJ}$ of energy? (d) The lattice energy of $\mathrm{ZnH}_{2}$ is 2870 $\mathrm{kJ} / \mathrm{mol}$ . Considering the trend in lattice enthalpies in the Group 2 $\mathrm{A}$ compounds, predict which Group 2 $\mathrm{A}$ element is most similar in ionic radius to the $\mathrm{Zn}^{2+}$ ion.

Consider the lattice energies of the following Group 2 $\mathrm{A}$ compounds: $\mathrm{Be} \mathrm{H}_{2}, 3205 \mathrm{kJ} / \mathrm{mol} ; \mathrm{MgH}_{2}, 2791 \mathrm{kJ} / \mathrm{mol}$ $\mathrm{CaH}_{2}, 2410 \mathrm{kJ} / \mathrm{mol} ; \mathrm{SrH}_{2}, 2250 \mathrm{kJ} / \mathrm{mol} ; \mathrm{BaH}_{2}, 2121 \mathrm{kJ} / \mathrm{mol}$
(a) What is the oxidation number of $\mathrm{H}$ in these compounds? (b) Assuming that all of these compounds have the same three-dimensional arrangement of ions in the solid, which of these compounds has the shortest cation-anion distance? (c) Consider BeH $_{2} .$ Does it require 3205 kJ of energy to break one mole of the solid into its ions, or does breaking up one mole of solid into its ions release 3205 $\mathrm{kJ}$ of energy? (d) The lattice energy of $\mathrm{ZnH}_{2}$ is 2870 $\mathrm{kJ} / \mathrm{mol}$ . Considering the trend in lattice enthalpies in the Group 2 $\mathrm{A}$ compounds, predict which Group 2 $\mathrm{A}$ element is most similar in ionic radius to the $\mathrm{Zn}^{2+}$ ion.

Key Concepts

Periodic Trends and Ionic Size Comparison

Periodic trends in the periodic table allow for the comparison of ionic sizes across different elements, such as within the Group 2A elements. Understanding these trends helps predict similarities in ionic radius between ions of different elements by considering factors like the effective nuclear charge and electron shell structures.

Lattice Energy

Lattice energy is the energy change that occurs when gaseous ions come together to form an ionic solid. It quantifies the strength of the electrostatic forces between the ions and is influenced by both the magnitude of the ionic charges and the distances between the ions; higher charges and shorter distances produce larger lattice energies according to Coulomb’s law.

Oxidation State

The oxidation state is a formalism that assigns a charge to an atom within a compound as if all bonds were completely ionic. This concept is essential for understanding the chemical behavior of compounds, particularly for determining the distribution of electrons and the types of ionic interactions present in the substance.

Ionic Radius and Cation-Anion Distance

The ionic radius measures the size of an ion and is crucial in determining the distance between cations and anions within a crystal lattice. A smaller cation will result in a shorter cation-anion distance, which typically leads to stronger electrostatic attractions and higher lattice energies.

Energy Sign Convention in Lattice Formation

The sign convention for lattice energy indicates that energy is released when an ionic solid forms from its constituent gaseous ions, making the formation exothermic. Conversely, breaking apart the solid into its ions requires an input of energy equal in magnitude to the lattice energy, reflecting the stability of the ionic lattice.

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