melting points

explain why magesium oxide has a high melting point

MgO has a giant ionic lattice structure which has strong electrostatic attraction between oppositely charged ions. this requires a lot of energy to overcome this (for the bonds to break), hence the high melting point.

explain why sodium has a high melting point

Sodium has a giant metallic structure which has strong electrostatic forces between the positive ions and the delocalised electrons. this requires a lot of energy to overcome this (for the bonds to break), hence the high melting point

explain why water has a low melting point

water has a simple covalent structure and there are only weak intermolecular forces holding the molecules together. only a little amount of energy is required to overcome them, hence the low melting point

explain why diamond has a high melting point

diamond has a giant covalent structure. the carbon atoms are held together by strong covalent bonds. therefore lots of energy is required to overcome these bonds, hence the high melting point.