Question

`"MgF"_2` has a melting point of 1263°C, while `"MgO"` has a melting point of 2852°C. Why is there such a significant difference in melting points?

Answer 1

Consider Coulomb’s law of electrostatic attraction....

Explanation:

You will have to look up the formula, but the force of attraction varies inversely with the SQUARE of the distance separating the charges, but varies proportionally to the PRODUCT of the charges. And thus an ionic species composed of ions with GREATER than unit charge, such as applies to the magnesium oxide salt, should develop a greater electrostatic force of attraction, than a salt with only unit charges...

And this is probably the reason why most oxides are prodigiously insoluble.