Question

Arrange the following compounds in order of highest to lowest lattice energy: LiF, RbBr, NaCl?

1) LiF, RbBr, NaCl
2) NaCl, RbBr, LiF
3) RbBr, NaCl, LiF
4) NaCl, LiF, RbBr

Answer 1

1) LiF, RbBr, NaCl

Step-by-step explanation:

Ionic compounds form crystal lattices held together by electrostatic forces, and lattice energy is a measure of the strength of these forces. The lattice energy is directly proportional to the product of the charges of the ions and inversely proportional to the distance between their centers.

In this case, we have LiF, RbBr, and NaCl. The ions in LiF, lithium (Li⁺) and fluoride (F⁻), have higher charges than those in RbBr (rubidium, Rb⁺, and bromide, Br⁻) and NaCl (sodium, Na⁺, and chloride, Cl⁻). Since lattice energy increases with the magnitude of the charges, LiF will have the highest lattice energy.

Additionally, size matters. Smaller ions have a stronger electrostatic attraction due to shorter distances between them. Li⁺ and F⁻ ions are smaller compared to Rb⁺ and Br⁻ ions, and Na⁺ and Cl⁻ ions.

Consequently, LiF has the smallest ion size and the shortest distance between ions, further contributing to its higher lattice energy. RbBr, with larger ions and a greater distance between them, will have the lowest lattice energy among the three. Therefore, the correct order is LiF > NaCl > RbBr.

Answer 2

The correct order from highest to lowest lattice energy for LiF, RbBr, NaCl is LiF (with the smallest ions), followed by NaCl, and then RbBr (with the largest ions).

Step-by-step explanation:

To arrange the following compounds in order of highest to lowest lattice energy: LiF, RbBr, NaCl, we need to consider two main factors: the charges on the ions and their radii. Lattice energy increases with higher ionic charges and decreases as ionic radii increase. Since all given compounds are binary ionic compounds with similarly charged ions (+1 and -1), the size of the ions becomes the determining factor.

Considering the size of the ions, Li+ is smaller than Na+, which is in turn smaller than Rb+. Also, F- is smaller than Cl-, which is smaller than Br-. Therefore, the compound with the smallest ions and subsequently the highest lattice energy is LiF, followed by NaCl, and the compound with the largest ions and the lowest lattice energy is RbBr. The correct order from highest to lowest lattice energy is 1) LiF, NaCl, RbBr.