Explain the trend in the lattice energies of the alkaline earth metal oxides.
Solution 43 E Step 1 of 1 We are considering oxides of elements belonging to the same group (II A). We know that the ionic radii increases while we pass from the top to the bottom of a group (it happens the same if we consider the atomic radii). Moreover, we know that lattice energy depends on the size of anions and cations that are in the compound. In fact there’s a reverse proportionality between dimensions and energy: the bigger the dimension, the smaller the energy and vice-versa. Since Mg is the atom with smaller dimensions, we can expect that MgO has the highest lattice energy for this group of oxides. Since Ba is the atom with the bigger dimension, we can expect the lowest lattice energy for this group of oxides. Obviously Ca and Sr have intermediate dimensions respect to Mg an Ba, thus we can even expect intermediate values of lattice energy, but CaO has the more negative value than SrO because Ca is smaller than Sr.