What is the difference between poly-atomic ion and molecular ion?

1 Answer
Truong-Son N.
Apr 22, 2018

Well, polyatomic ions do not have to be molecular.

Molecular [polyatomic] ions can be, for instance, #"NH"_4^(+)#, #"CO"_3^(2-)#, #"PO"_4^(3-)#, #"BrO"_3^(-)#, etc., since they contain bonded elements that have similar electronegativities (within #1.0# or less).

[They are molecular in the sense that the bonds are molecular but ions in the sense that they have a charge overall.]

[General] polyatomic ions could include molecular ions (e.g. the above), and non-molecular ions such as #"MnO"_4^(-)#, #"MnO"_4^(2-)#, #"CrO"_4^(2-)#, or #"Cr"_2"O"_7^(2-)#. Those contain central atoms with low electronegativity compared to #"O"#, and hence are non-molecular.

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