Question

1. Calculate the attractive bonding force for NaF and for MgO when the ions just touch. Based on the attractive bonding force, which compound would you expect to have the higher melting temperature and why?

Answer 1

Answer:

The attractive force is negative and MgO has a higher melting point

Explanation:

From Couloumb's law:

Energy of interaction, E = k $\frac{q1q2}{r}$

where q1 and q2 are the charges of the ions, k is Coulomb's constant and r is the distance between both ions, i.e the atomic radii of the ions.

If you look at Coulomb's law, you note that in the force is negative (because q1 is negative while q2 is positive).

In addition to that, the compounds MgO and NaF have similar combined ionic radii, then we can determine the melting point trend from the amount of energy gotten

The melting point of ionic compounds is determined by 1. charge on the ions 2. size of ions. while NaF has smaller charges (+1 and -1), MgO (+2 and -2) has larger charges and greater combined atomic radii. This implies that the compound with greater force would have a higher melting point.

Hence the compound MgO would have a higher melting point than NaF.