Final answer:
Lattice energy is typically a positive value indicating an exothermic reaction, with lots of energy released when an ionic compound like SrO forms.
Step-by-step explanation:
The question is asking why SrO has a negative lattice energy. Lattice energy is the energy released when oppositely charged ions in the gas phase come together to form a solid. In the case of SrO, the correct answer is not listed in the given options, but we can discern the most accurate explanation. Lattice energy is typically positive because it's an exothermic process, meaning energy is released when the ionic solid forms. A negative value for lattice energy might suggest an endothermic process, but this is unlikely for ionic compounds like SrO. The lattice energy of an ionic compound depends on the charges on the ions and the distance between them, as well as crystal structure and polarizability. In SrO, which has a high melting point, the strong electrostatic attractions between Sr2+ and O2- ions result in a large, negative (exothermic) lattice energy—meaning a lot of energy is released when SrO forms from its constituent ions.
In ionic compounds, the lattice energy is determined by the product of the ionic charges and the internuclear distance. SrO has a negative lattice energy because of the strong repulsive forces between ions. These repulsive forces are due to the small size of the ions in SrO.