Electronegative Ions :
The species which carry negative charge on them (or) The species formed by gain of electrons by an atom are called Electronegative Ions. (or) Anions.
Negative valence:
Some elements tend to take electrons from other elements so as to have eight electrons in their outermost orbit. The number of electrons accepted by an atom of an element is its negative valency.
An ion or radical formed by the accepting of one electron or two electrons or three electrons for its stability is called as monovalent negative ion or divalent negative ion or trivalent negative ion respectively.
Example: \(C{l^ - },\,{O^{2 - }},\,{N^{3 - }}\,,SO_4^{2 - },\,O_2^{2 - }\)
Illustration -1 Explain the variable valencies of phosphorous
Solution :Phosphorous shows two valencies they are 3,5.
Becuase of phosphorous shows three unpaired electrons in first excited state so valency is 3.
Phosphorous shows five unpaired electrons in second excited state.So valency is 5