the lattice energy for MgCl2 is -2326 kj/mol, which is much higher than that for NaCl which has a lattice energy of -786 kj/mol. Why is this so? Give at least two contributing factors.
ionic charge
ionic radius
Can you explain to me why?
Mg^2+ is twice the charge of Na^+ so the effect is 4x as much. (2^2 = 4)
The Mg^2+ ion is smaller than the Na^+ and the closer the ions are togther the tougher it is to pull them apart.
The difference in lattice energy between MgCl2 and NaCl can be attributed to several factors. Here are two contributing factors:
1. Charge of the ions: MgCl2 consists of Mg2+ and Cl- ions, while NaCl is composed of Na+ and Cl- ions. The magnitude of the charge on the ions affects the strength of the electrostatic attraction between them. In MgCl2, the Mg2+ ion has a higher charge compared to the Na+ ion in NaCl. The higher charge on the Mg2+ ion results in stronger attractions between the cation and anion, leading to a higher lattice energy.
2. Size of the ions: The size of the ions also plays a role in determining the lattice energy. In MgCl2, the Mg2+ ion is smaller compared to the Na+ ion in NaCl. Smaller ions are able to pack more closely together, resulting in higher lattice energy. This is because the closer proximity of the ions allows for stronger electrostatic interactions.
To calculate lattice energy, you can use the Born-Haber cycle or the Born-Lande equation. The Born-Haber cycle involves a series of steps, including ionization energy, electron affinity, enthalpy of sublimation, and enthalpy of hydration, which are summed together algebraically. The Born-Lande equation is a simplified formula that involves the product of the charges of the ions, the Avogadro constant, the Madelung constant (a factor accounting for the arrangement of ions in the lattice), and the charge and radius of the ions.
In this case, comparing the lattice energies of MgCl2 and NaCl, the higher charge on the Mg2+ ion and the smaller size of the Mg2+ ion compared to the Na+ ion contribute to the higher lattice energy of MgCl2.