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 identify the central atom, X. Arrange your answers in order increasing n.

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We’re asked to identify the central atom, X for each of these ions where n = 1-, 2- and 3- based on the given Lewis structure of the polyatomic oxyanion:

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.

We know that the element, X comes from the third period (Na to Ar) and when it is bonded to 4 O's it forms a polyatomic oxyanion



Recall that a polyatomic oxyanion is a molecule consisting of a nonmetal bonded to more than one Oxygen atoms (covalent bond).  This means that X cannot be a metal (metal + nonmetal = ionic bond)


To identify the atom, X for each charge n, we need to do these steps:


Step 1: Determine the number of valence electrons for the central atom, X for each charge, n

Step 2: Determine Group Number and corresponding element X for each polyatomic oxyanion


From the given Lewis structure, there are a total of [4 x 6] + 4 (bonds) = 32 valence e

**The line (—) represents a "bond" where 2 electrons are shared between two atoms

**Each dot represents 1 electron (for every O atom there are 6 dots = 6 e) 


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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 identify the central atom, X. Arrange your answers in order increasing n.

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What scientific concept do you need to know in order to solve this problem?

Our tutors have indicated that to solve this problem you will need to apply the Lewis Dot Structure concept. You can view video lessons to learn Lewis Dot Structure. Or if you need more Lewis Dot Structure practice, you can also practice Lewis Dot Structure practice problems.

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