Is the melting point of CaCl_ higher than that of \(\mathrm{NaCl}\) or lower? Explain your answer.

In the realm of chemistry, the melting point of an ionic compound is profoundly influenced by the charges of the ions it contains. When we look at compounds like Calcium Chloride (CaCl₂) and Sodium Chloride (NaCl), we find that CaCl₂ has a divalent cation (Calcium with a 2+ charge) and two monovalent anions (Chloride with a 1- charge each), while NaCl consists of monovalent ions (Sodium with a 1+ charge and Chloride with a 1- charge).

The greater the charge of the ions, the stronger the electrostatic force between them. This concept is essential for understanding why CaCl₂, with its 2+ cation, can form stronger ionic bonds compared to NaCl, leading to a higher melting point. Thus, the ionic charges directly relate to the compound's ability to resist thermal energy, influencing its melting point.

The Ionic radius, or the size of an ion, is another critical factor affecting the strength of the ionic bond and consequently the melting point of the compound. In our comparison between CaCl₂ and NaCl, we must note that sodium ions have a larger radius than calcium ions. A larger ionic radius often indicates that electrons are less tightly bound to the nucleus, resulting in weaker attraction between ions.

This means that compounds with smaller ions (and thus smaller ionic radii) can pack more closely together, producing a stronger electrostatic attraction. It also implies that CaCl₂, with its smaller calcium ions compared to the larger sodium ions in NaCl, will likely have a higher melting point due to the tighter and stronger interaction between its constituent ions.

Ultimately, the strength of ionic bonds is what determines the melting point of an ionic compound. Stronger ionic bonds require more energy to break apart, which correlates to a higher melting point. As previously discussed, Calcium Chloride has a cation with a higher charge (2+) and a smaller ionic radius compared to the Sodium ion in Sodium Chloride.

Consequently, the ionic bond strength in CaCl₂ is greater due to the higher charge intensity and the closer packing of ions allowed by the smaller ionic radius. This heightened bond strength suggests that CaCl₂ will have a higher melting point than NaCl, as it requires more thermal energy to overcome the strong electrostatic forces holding the lattice together.