Answer to Question #79077 in Atomic and Nuclear Physics for santhosh

Question

NaCl has a melting point of 800 ºC and MgO has a melting point of 2800 ºC.
How would you explain these facts?

Answer 1

Both MgO and NaCl exist as a giant ionic lattices where each oppositely charged ion is held in place by a strong electrostatic attractions. These ionic bonds are strong and require a large amount of thermal energy to overcome them and break the structure, enabling it to change state from a solid into a liquid. The ionic bonding in sodium chloride is between Na^+ and Cl^- ions whereas the ionic bonding in magnesium oxide is between Mg^2+ and O^2- ions. As the charge in the ionic lattice in magnesium oxide is two times as large, the ionic bonding is stronger so more energy is required to overcome the electrostatic attraction and break down the ionic lattice.