Question

Give reason : ionic compounds of the halogen contain singly charged $X^{-}$ ion and not doubly charged $X^{2-}$ ion.

Answer 1

For the formation of ionic compounds, one of the atoms should have high electron affinity.

Electron affinity is a property of an atom to accept an electron in its valence shell.  Compared to other elements, the halogens possess the "highest electron affinity". This property helps the halogens to get converted as anions and forming ionic bonds readily.

There are other elements that have high electron affinities and that are capable of forming ionic compounds like the elements of Group VI. These elements need to accept 2 electrons for the achievement of a stable configuration.  

During the process of accepting of electrons, one electron is added to the atom along with release of energy, thereby forming a single charged negative ion. This produced anion repels the next electron that is yet to be accepted by the atom. Hence, an energy greater than the repulsion has to be applied for adding the second electron.  

Therefore, double charged negative ions do not get formed in ionic compounds of halogens.