Problem. 67 says to rationalize the lattice energy values of each of these four compounds and discuss why they make sense relative to each other. So once we've discussed in previous problems, um, two aspects of an ionic compound that makes them relatively x author, Miss X if emmerich and regard to lattice energy our, um, e a charge on the ions and the size of the ions so hire charge usually leads to a more x a thermic Gladys energy. And a smaller size also leads to a higher, um, Gladys Energy. So in this case, um, first of all, it makes sense that, uh, the compounds containing calcium have a more x a thermic ah lattice energy, because calcium has a positive to charge and selenium and Tillery, um, have a negative to charge. This is a comparison to sodium, which has a positive one charge. So for each of these compounds, the higher charge on calcium leads toothy kind, greater lattice energy. Um, and then, with respect, thio um, the compounds containing selenium versus terrarium um uh, selenium iss smaller, then delirium. And in general, like I said, smaller ions tend to have larger lattice energy because two ions can, um can basically get closer together, and their attraction is much higher. So for that reason, it also makes sense that the lattice energy on compounds containing selenium versus Hillary um is higher. Um, And so in that case, um, it does make sense that the order of lattice energy is that calcium, um bound to selenium is the highest because it has the largest charge and the smallest ions, followed by calcium pounded Towler M and then sodium in that order.