# Homework Help: Lattice Energy

1. Dec 11, 2007

### physstudent1

1. The problem statement, all variables and given/known data

Order the following compounds in order of increasing lattice energy:

AlN, BaTe, KCl, Rb2Se

2. Relevant equations

3. The attempt at a solution
Ok I know that as the distance between the two nuclei decreases and as the charge of the cation and anion increase the lattice energy increases, so I thought the order would be

KCl, BaTe, Rb2Se, AlN however this is wrong...I'm not sure why but I think the Rb2Se is confusing me anyway I would appreciate it if someone could help me out here

Last edited: Dec 11, 2007
2. Dec 11, 2007

### Kushal

i think lattice energy of BaTe is higer than that of Rb2Se.

the product of charges is higher in BaTe and the sum of ionic radii are quite nearly the same, (135+97)pm and (152+50)pm respectively. they have a smaller effect compared to the product of charges.

anyway, you can calculate the relative lattice energy.

L.E. = k (product of charges)/(sum of ionic radii)

k is a constant, it's gonna be the same for all the ionic compounds, ignore it.
just divide the product of charges by the sum of ionic radii.