Why the melting point of magnesium oxide is much higher than sodium chloride?

Answer 1

Melting point is dependant upon packing and intermolecular forces. Magnesium and Sodium are both metals, and therefore have metallic bonding. Both are a lattice of positively charged ions surrounded by a sea of delocalized electrons. Magnesium however has 2 delocalized electrons for every one magnesium atom, it therefore forms smaller ions than Sodium, which pack more closely together. The higher number of delocalized electrons in magnesium also pull the positively charged even closer together.

Answer 2

Solid magnesium has an atomic structure of positive ion lattice surrounding by a "cloud" of free-moving dissociated electrons. These electrons hold the ions together in the lattice and must be disrupted to allow magnesium to melt. In iodine the only inter-molecular forces are Van der Waals forces which are weak and easy to disrupt and this means that the amount of energy required to melt iodine is much lower and as such its melting point is much lower.

Answer 3

The sodium ion has a 1+ charge and the chloride ion has a 1- charge.

By comparison the magnesium ion has a 2+ charge and the oxide ion a 2- charge.

Because the charge difference is greater in magnesium oxide, the forces of attraction between the ions are greater. This makes the ions harder to move from their positions which is what happens when a substance melts.

Additionally, the magnesium ion is smaller than the sodium ion and the oxide ion smaller than the chloride ion. This increases the density of the charges and makes forces of attraction even stronger.

Answer 4

Magnesium has two valence electrons where sodium has one. Therefore magnesium can form metallic bonds with more free electrons than sodium. Hence, magnesium has a higher melting point and boiling point.

Answer 5

The crystal structure is a main factor in the melting point of a compound. Ca has several crystal structures and Mg has a closed pack crystal structure.

Answer 6

ok as we saw that ions present in magnesium oxide are double charged while in sodium chloride ions are singly charged so mgo has heigher melting point.

Answer 7

Because Na has fewer protons & Na has a bigger ion, so there is smaller attraction between nucleus & delocalised electrons

Answer 8

Basically, it is because this is a ionic compound in a strong crystalline structure. All ionic compounds are of high melting points outside of solution.