Question

Which of the following compounds has the lowest lattice energy? Ca(OH)2, KBr, InAs, SrSe

Answer 1

@AJ01 can you help with this?

Answer 2

Alright then.
Lattice energy is the energy given off when two ions in the gaseous state react. The energy is greater when the ions are smaller, because electrostatic attraction is greater, since there is more approximation to the nucleus of the opposite ion.
For this case, let us see which cation in the largest. Remeber down the group, ionic radii increases and accross the period, it decreases from G1 to G4 and G5 has the widest ion from which decreases from G5 to G8.
The largest cation is therefore is K.
The largest anion is As.
However we need to find the most perfect combination of 2 possible largest ions to have the lowest lattice energy. That would be KBrfor me, because Sr is way smaller than K, despite that that the Se is larger, but I will bet for KBr.