Question

Which compound has maximum lattice energy

Answer 1

Lattice energy is given by the product of the charges on the ions, divided by the sum of their ionic radii.Let's compare K2O and Li2O first.K has a larger radius than Li because it's lower down in the periodic table. It also has the same charge (+1) as Li. Since the anion (O) is the same in both compounds, the lattice energy of Li2O is larger than K2O. This is because dividing the product of their charge by a larger radius gives a smaller value of lattice energy.Rubidium is below K in the periodic table and thus its ionic radius is really huge. Plus, S is below O in the table and it has a larger ionic radius. Thus, even though Rb and S have the same charges as Liand O (+1, -2) the lattice energy of Rb2S will be much much lower than Li2O and K2O due to the huger ionic radius. After all, dividing a constant number (+1 times -2) by a larger value of radius will give a smaller number ie value of lattice energy.