Question

Consider the Lewis structure for the polyatomic oxyanion shown here, where X is an element from the third period (Na−Ar). By changing the overall charge, n, from 1- to 2- to 3- we get three different polyatomic ions.
Element X is surrounded by 4 oxygen atoms bonded to it with full octets.


A)For each of these ions identify the central atom, X. Arrange your answers in order increasing n.

B)For each of these ions determine the formal charge of the central atom, X. Arrange your answers in order increasing n.


I really have no idea how to solve this. Any help would be greatly appreciated!

Answer 1

Hey there!

A ) PO₄³⁻

The element exhibits resonance (4 times) as there is a double bondwith 1 oxygen and a single with the other 3 oxygen. This switchesin each resonance structure. (I know its weird b/c  I leaves Phosphorus with 10 electrons surrounding it)

b) SO₄²⁻

Sulfur is the central atom  ,double bond 2 oxygens so that they can only have 4 valence electrons ( the little dots around the oxygen )  ,single bond 2 oxygens ( So that they have 6 valence electrons )

Formal charges are 0 for the two double bonded oxygens [ 6-6 = 0 ]and 0 for the sulfur [ 6-6=0 ]

But the oxygens are -1 [ 6-7 = -1 ]

Since there are two of them, there is a negative charge of -2

Bracket the whole structure and on the top right of the outside ofthe brackets write 2- and include a - (negative sign) next to eachof the single bonded oxygens

Don't forget there are resonance structures. The double bonds canbe placed around any of the oxygens

Hope that helps!