Which of the following compounds should have the greatest lattice energy?
CaO NaCl CrN MgBr2
The lattice energy of a compound is determined by the charges of the ions and the distance between them. The greater the charges and the smaller the distance, the greater the lattice energy.
Looking at the compounds:
CaO has a +2 charge on the Ca ion and a -2 charge on the O ion.
NaCl has a +1 charge on the Na ion and a -1 charge on the Cl ion.
CrN has a +3 charge on the Cr ion and a -3 charge on the N ion.
MgBr2 has a +2 charge on the Mg ion and a -1 charge on the Br ion.
Out of these compounds, CrN should have the greatest lattice energy because it has the highest charges on the ions (+3 and -3). The other compounds have smaller charges on the ions, so their lattice energies will be lower.