Despite having the same ionic nature, magnesium oxide and sodium oxide has a difference of 2000oC between their melting points. Explain why.

The difference in melting points between magnesium oxide and sodium oxide, despite both being ionic, can be explained by the difference in their ionic bonds' strength.

1. Ionic Bond Strength: The strength of an ionic bond is determined by the charge on the ions and the size of the ions. Magnesium oxide (MgO) has a +2 and -2 charge on the magnesium and oxygen ions respectively, while sodium oxide (Na2O) has a +1 and -2 charge on the sodium and oxygen ions respectively. The higher charge on the magnesium and oxygen ions in MgO results in a stronger ionic bond compared to Na2O.

2. Ionic Size: Magnesium ions are smaller than sodium ions. The smaller size of magnesium ions allows them to get closer to the oxygen ions, resulting in a stronger ionic bond in MgO compared to Na2O.

3. Lattice Energy: The stronger ionic bond and smaller ionic size in MgO result in a higher lattice energy compared to Na2O. Lattice energy is the energy required to break the ionic bond and convert the compound into gaseous ions. The higher the lattice energy, the higher the melting point of the compound.

Therefore, due to the stronger ionic bond and higher lattice energy, magnesium oxide has a significantly higher melting point compared to sodium oxide.