Why do ionic compounds have high melting and boiling points?

Ionic compounds have high melting and boiling points due to the strong electrostatic forces of attraction between their positive and negative ions.

Ionic compounds are formed when a metal reacts with a non-metal. They are composed of positive and negative ions, which are held together by strong electrostatic forces of attraction. This force of attraction, also known as ionic bonding, is very strong and requires a lot of energy to overcome. This is the primary reason why ionic compounds have high melting and boiling points.

The strength of the ionic bond is determined by the charge on the ions and the size of the ions. The greater the charge and the smaller the size of the ions, the stronger the ionic bond. For example, magnesium oxide has a higher melting point than sodium chloride because magnesium and oxygen ions have greater charges than sodium and chloride ions, and are also smaller in size. This results in a stronger ionic bond and hence a higher amount of energy required to break the bond, leading to a higher melting point.

The arrangement of ions in an ionic compound also contributes to its high melting and boiling points. Ionic compounds form a giant ionic lattice structure, where each ion is surrounded by ions of the opposite charge. This maximises the attraction between the ions and increases the stability of the structure. When heat is applied, it takes a large amount of energy to disrupt this stable structure, hence the high melting and boiling points.

In summary, the high melting and boiling points of ionic compounds can be attributed to the strong electrostatic forces of attraction between the ions, the charge and size of the ions, and the giant ionic lattice structure of the compounds. These factors collectively result in a large amount of energy being required to break the ionic bonds, leading to high melting and boiling points.