Largest Lattice Energy: NaCl, CaO, Li2O, or CaCl2?

[fk378]

Homework Statement

Which one of the following ionic compounds has the largest lattice energy?

NaCl
CaO
Li2O
CaCl2

Homework Equations

Ionic/Atomic size
The smaller the ionic size, the larger the lattice energy.
Size increases from right to left, increases top to bottom of periodic table

The Attempt at a Solution

I've tried to compare the like ionic compounds, such as NaCl with CaCl2 but I can't seem to figure out which is bigger--Na+ or Ca2+

Am I approaching this incorrectly?

 

[ace123]

Well if your losing electrons then the atomic size would what?

 

[fk378]

Loss of electrons means smaller atomic radius. But Na and Ca don't have the same number of protons so isn't there another way to have to look at it?

 

[ace123]

Well the loss of electrons makes the radius smaller. You know Na is one of the bigger elements size wise right? And the size decreases as you go across the periodic table. The protons don't attract the valence electrons as much as the core electrons b/c of shielding. Do you get it now?

 

[Kushal]

are you considering charges?

L.E. is directly proportional to product of charges on ions but inversely proportional to sum of ionic radii.

hope it helps