sheezle

and Aluminum (+3) would have a smaller ionic radius than both the Na and Mg ions -- but because the diff in elecneg between aluminum and oxygen is smaller than the diff in elecneg between magnesium and oxygen, it ends up having a lower boiling point. is that correct? what are the deciding factors that determines an ionic compound's melting/boiling points? i know in explaining the ionization energy of elements it's first distance, then nuclear charge, then electron-electron repulsion, so i wonder if there's a similar "rubric" to explain m.p and b.p. as well...

hmm, but the difference in elecneg. between sodium and oxygen is larger than the difference in elecneg between magnesium and oxygen, yet MgO has a higher melting point than Na2O as well.

this isn't a question from homework -- really it is out of curiosity. why is the melting point of Al2O3 lower than the melting point of MgO? i did chance across this problem in a homework packet but was told to "ignore it for now" by my chem teacher because we would learn it later, but i am curious, and would like an answer now! thanks in advance. btw i have just finished learning about bonding in class. (HL chem)