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

FREE Expert Solution

Recall: Formal charge is given by:

F.C. = # of val. e  – (# of bonds + # of lone pair e)

Based on the given Lewis structure, there are a total 32 valence electrons. We can use this information to determine the number of valence electrons of the unknown element.

For the polyatomic ion with a charge of –1: Not counting the electrons from the charge of the ion, the polyatomic ion has 32 – 1 = 31 valence electrons. Subtracting the valence electrons of the oxygens gives us:

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Problem Details
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.

A central X is single bonded left, right, above, and below to O; each O has three pairs of dots.  The molecule as a whole has a negative charge of unknown magnitude.

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

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