We can define average bond enthalpies and bond lengths for ionic bonds, just like we have for covalent bonds. Which ionic bond is predicted to be stronger, \(\mathrm{Na}-\mathrm{Cl}\) or \(\mathrm{Ca}-\mathrm{O}\) ?

To determine the type and strength of an ionic bond, we need to know the charges of the ions involved. For each of the compounds, we will look at the periodic table and find the charges of the ions. For \(\mathrm{NaCl}\): - \(\mathrm{Na}\) is in group 1, so it has a charge of +1 when it forms an ion. - \(\mathrm{Cl}\) is in group 17 (7A), so it has a charge of -1 when it forms an ion. For \(\mathrm{CaO}\): - \(\mathrm{Ca}\) is in group 2, so it has a charge of +2 when it forms an ion. - \(\mathrm{O}\) is in group 16 (6A), so it has a charge of -2 when it forms an ion.

From the charges of the ions, we can determine which ones have a stronger electrostatic attraction, considering that the higher the charges are, the stronger the bond. In \(\mathrm{NaCl}\), the charges are +1 and -1. In \(\mathrm{CaO}\), the charges are +2 and -2. Since \(\mathrm{CaO}\) has a higher charge on both ions compared to \(\mathrm{NaCl}\), it appears that \(\mathrm{CaO}\) might have a stronger bond. However, we also need to take ion sizes into account to make a definitive conclusion.

Larger ions will have weaker bonds, as the electrostatic forces decrease with increasing size. Looking at the periodic table, we can infer the sizes of the ions involved: - \(\mathrm{Na}\) and \(\mathrm{Ca}\) are both in period 3. However, since \(\mathrm{Ca}\) is in group 2 and \(\mathrm{Na}\) is in group 1, \(\mathrm{Ca}\) is larger than \(\mathrm{Na}\). - \(\mathrm{O}\) and \(\mathrm{Cl}\) are both in period 2. Since \(\mathrm{O}\) is in group 16 (6A) and \(\mathrm{Cl}\) is in group 17 (7A), \(\mathrm{O}\) is smaller than \(\mathrm{Cl}\). Comparing the sizes of the ions involved in each bond: - \(\mathrm{Na}\) is smaller than \(\mathrm{Ca}\). - \(\mathrm{O}\) is smaller than \(\mathrm{Cl}\). As a result, the \(\mathrm{NaO}\) bond involving the smaller ions might be expected to be stronger than the \(\mathrm{Ca-Cl}\) bond.

Taking both charges and ion sizes into account, we can make a prediction about which ionic bond is stronger. The \(\mathrm{Ca-O}\) bond has a higher charge and involves smaller ions, which both contribute to a stronger bond. Therefore, we predict that the \(\mathrm{Ca-O}\) ionic bond is stronger than the \(\mathrm{Na-Cl}\) bond.