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 draw a Lewis structure that makes the formal charge on the central atom equal to zero.

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We are asked to draw a Lewis structure that makes the formal charge on the central atom equal to zero

We are given that 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.

To do so, we need to do the following steps:


Step 1: Determine the number of valence electrons and the identity of X.

Step 2: Determine the formal charge of X.

Step 3: Draw the Lewis structure for the molecule.

Step 4: Draw the Lewis structure that makes the formal charge on the central atom equal to zero.


Recall that the formula for the formal charge is:


F.C.=Group Number-(Bonds+Nonbonding Electrons)



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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 draw a Lewis structure that makes the formal charge on the central atom equal to zero.

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