need help on chem question

[QatarOwnz]

Predict whether the lattice energy of MgO is more or less exothermic than the lattice energy of MgS.
Justify your answer in terms of the sizes and the charges of the ions involved.

also see attachment

 

[Blueberryavalanche47]

We discussed this question in class once actually... It's a bit tough :/
But basically
think about MgS... how many valence electrons does Magnesium and Sulfur have?
Mg: 2
S: 2

now how about Magnesium and Oxygen?
Mg: 2
O: 2

so it has nothing to do with 2+ 2- electrostatic force of attraction because they both have a 2+ 2- attraction.
So it must be their sizes. The Oxygen has 2 shells meanwhile Sulfur has 3 shells so Sulfur will have a larger ionic radius.
So the difference between MgO and MgS is the anion. The oxide ion is smaller than the sulfide ion. Thus, the distance separating the ions' nuclei should be smaller for MgO than for MgS so then the lattice energy should therefore be greater for MgO than for MgS so, MgO is more exothermic.

I didn't get this at first either lol

 

[abood123980]

Predict whether the lattice energy of MgO is more or less exothermic than the lattice energy of MgS.
Justify your answer in terms of the sizes and the charges of the ions involved.

also see attachment

oxygen has a smaller ionic radius.
oxygen has higher charge density.
electrostatic attractions in mgo are stronger and need more energy to be broken down.