Sodium oxide has a high melting point because of the strength ofits bonds. Due to having strong bonds, they cannot be broken veryeasily. Magnesium chloride is ionic compound. There is a strong electrostatic force of attraction between 2 chloride atoms and 1 magnesium atom.
Because it retains its strength at very high temperatures. It is considered a refractory material with a melting point of 6500 degrees F. It is also very non-reactive with other materials that might be put into the furnace and is even used to make crucibles - containers used to melt other substances.
