Question

Which one $PCl_{4}^{+}$ and $PCl_{4}^{-}$ is not likely to exist and why?

Answer 1

The basic properties of the anions and cations where the atom is electropositive (electron deficient) or electronegative (electron rich) and also the octet rule will give the required answer to this question.

Complete answer:
We have studied the basic concept of chemistry which tells about some of the basics of the atoms and its properties such as the electropositivity, electronegativity and so on. We have also studied about the octet rule.
We shall now discuss in detail about these so that we can reach the required answer.
- Octet rule states that the atoms tend to form compounds in ways that give them eight valence electrons and therefore which is the electronic configuration of a noble gas.
- The chlorine atom is electronegative, that is it is rich in electrons and hence donates the electrons to the electron deficient atom that is phosphorus.
- But here, when the phosphorus atom accepts 3 electrons from the 3 chlorine atoms, the octet structure is complete and hence will be unable to take one more electron from the remaining $C{{l}^{-}}$ ion.
- Thus, the formation of the negative compound that is $PCl_{4}^{-}$ is difficult.
- Now, on moving down the group, the stability of the lesser oxidation state increases, that is +5 oxidation state decreases and that of +3 oxidation state increases.
- Thus, the formation of the positive compound that is $PCl_{4}^{+}$ is more likely to be formed.

Note:
Note that the chlorine atom belongs to the third period and seventeenth group which is basically called as the halogen group and thus is a highly reactive element which is an electronegative element.