Metallic bonding is the strong attraction between closely packed positive metal ions and a 'sea' of delocalised electrons. The attraction between the metal ions and the delocalised electrons must be overcome to melt or to boil a metal. These attractive forces are strong, so metals have high melting and boiling points.
In respect to this, why is the melting point of magnesium higher than that of sodium?
The nuclear charge of magnesium is higher than that of sodium. Magnesium has more electrons than sodium. Both these mean that there is a stronger electrostatic attraction between the positive magnesium ions and its delocalised electrons in the giant metallic lattice. Therefore more energy is required to overcome it.
Why do ionic compounds have a high melting point?
High melting and boiling points - Ionic bonds are very strong - a lot of energy is needed to break them. So ionic compounds have high melting and boiling points. Conductive when liquid - Ions are charged particles, but ionic compounds can only conduct electricity if their ions are free to move.
Why is the melting point of sodium chloride high?
Sodium chloride has a high melting and boiling point. There are strong electrostatic attractions between the positive and negative ions, and it takes a lot of heat energy to overcome them. Ionic substances all have high melting and boiling points.