Which compound has the largest lattice energy? NaF b. Al2O3 c. MgO d. CaS e. CaO
The Correct Answer and Explanation is:
The compound with the largest lattice energy is Al₂O₃ (aluminum oxide).
Lattice energy is the energy released when one mole of an ionic compound is formed from its ions in the gas phase. Larger lattice energy typically results from stronger electrostatic attractions between ions. These attractions depend on two factors:
- Charge on the ions: The larger the charge, the stronger the electrostatic attraction. The lattice energy increases with the charge of the ions involved in the formation of the ionic lattice. For example, Al³⁺ has a higher charge than Na⁺, Ca²⁺, Mg²⁺, and O²⁻.
- Ionic radius: The smaller the ions, the closer they can pack together, leading to stronger attraction and a higher lattice energy. Smaller ions result in a greater charge density, which enhances the lattice energy.
Let’s look at each compound:
- NaF (Sodium fluoride): Sodium (Na⁺) has a +1 charge, and fluoride (F⁻) has a -1 charge. Although fluorine is small, the lattice energy is lower compared to others because of the low charge on sodium.
- Al₂O₃ (Aluminum oxide): Aluminum (Al³⁺) has a +3 charge, and oxygen (O²⁻) has a -2 charge. The high charges on both ions, especially the highly charged Al³⁺, lead to a very strong electrostatic attraction and thus a high lattice energy.
- MgO (Magnesium oxide): Magnesium (Mg²⁺) has a +2 charge, and oxygen (O²⁻) has a -2 charge. Magnesium has a higher charge than sodium, but its lattice energy is still lower than that of Al₂O₃ due to the lower charge on Mg²⁺ compared to Al³⁺.
- CaS (Calcium sulfide): Calcium (Ca²⁺) has a +2 charge, and sulfur (S²⁻) has a -2 charge. Although the ions are larger than Mg²⁺ and O²⁻, the lattice energy is still lower because of the larger ionic radii of Ca²⁺ and S²⁻.
- CaO (Calcium oxide): Calcium (Ca²⁺) and oxygen (O²⁻) have charges of +2 and -2, respectively, similar to MgO, but calcium ions are larger, leading to a lower lattice energy than Al₂O₃.
Therefore, Al₂O₃ has the largest lattice energy due to the high charges on both aluminum and oxygen, resulting in the strongest ionic attraction.
