Which ionic compound has highest lattice energy

Question

KBr

CaO

BaO

CrS

FeP

Which would have highest lattice energy and why?

Answer 1

Lattice energy (LE) is dependent on the changes on the ions and the atomic radii of the ions. The greater the charge, the greater the LE. The smaller the atomic size, the greater the LE. This can be seen using Coulomb’s Law, F = q₁q₂ / r²

FeP has ions with 3+ and 3- charges which is greater than any of the others, so it will have the greatest LE.

Next we look at CaO, BaO and CrS which all have 2+ and 2- charges. So we look at atomic sizes. The smallest is Cr, followed by Ca and Ba. Also S is smaller than O, so here we have CrS greater LE than CaO greater than BaO.

Finally, KBr will have the lowest LE because it is made up of +1 and -1 ions.

summary of LE:

FeP > CrS > CaO > BaO > KBr