Final answer:
The compounds can be ranked from greatest to least in lattice energy as follows: CaCl₂ > CaO > MgCl₂ > MgO.
Step-by-step explanation:
The lattice energy is a measure of the strength of the ionic bonds in a compound. It is directly proportional to the product of the charges of the ions and inversely proportional to the distance between them. In this case, we need to compare the lattice energies of CaO, MgO, CaCl₂, and MgCl₂. To determine the order of lattice energy, we need to compare the charges of the ions and consider their sizes.
CaO contains Ca²+ and O²- ions. The charge on the Ca²+ ion is higher than the charge on the Mg²+ ion in MgO. Therefore, CaO would have a higher lattice energy than MgO.
CaCl₂ contains Ca²+ and Cl- ions. The charge on the Cl- ion is greater than the charge on the O²- ion in CaO. Therefore, CaCl₂ would have a higher lattice energy than CaO.
MgCl₂ contains Mg²+ and Cl- ions. The charges on the ions in MgCl₂ are the same as in CaCl₂, but the size of the Mg²+ ion is smaller than the size of the Ca²+ ion. Therefore, CaCl₂ would have a higher lattice energy than MgCl₂.
Therefore, the compounds can be ranked from greatest to least in lattice energy as follows: CaCl₂ > CaO > MgCl₂ > MgO.