Resonance Structures of PO4 (3-)

• oceanflavored
In summary, the student is studying for an AP Chemistry exam and is stuck on a question involving drawing resonance structures for PO4 (3-). They have attempted to draw the Lewis structure, but are unsure of how to incorporate resonance into their diagram. They are seeking assistance in understanding the concept of resonance and how it applies to this specific problem.

Homework Statement

i am studying for my apchem exam in may.and got stuckup on a question. it's just a little exercise.so the answers aren't there.but ok here it is;
give the resonance structures of PO4 (3-) and there's supposed to be four

none?

The Attempt at a Solution

i started drawing it so..
PO4 (3-) = 5 + (6*4) +3 = 32/2 = 16 pairs of electrons so...

O
|
O -- P --- O
|
O

so there's the single bonds (8 electrons: octet rule) for P and then 6 electrons around each O to complete O's octet rule.
and my problem is...where's the dang resonance structure? because everyone gets their electrons.and is happy. unless of course P has an expanded octet and gets more than 8?
'ppreciate it alottttt.

sorry.

ewwww.my molecular structure messed up. hopefully you guys will understand what I'm talking aboutt.
<- i like that smiley

how about one double bound, two single bound and another oxygen atom just dangling around, sucking the electron from the P and not sharing any?

I might be wrong though... it's been a while since that ap chem exam...

tim_lou said:
how about one double bound, two single bound and another oxygen atom just dangling around, sucking the electron from the P and not sharing any?

This isn't a resonance structure - by definition, connectivity must remain unchanged; you can only move electrons.

So you can take a lone pair of electrons from an oxygen and make another bond (thus creating a P=O) and leave the others unchanged - this can be done for each oxygen, creating four different resonance structures. Although this gives P ten valence electrons, it results in a formal charge of 0 for both P and O.

Just a reminder to those answering the question...try not to just offer answers (especially ones you're uncertain of) and help guide those asking the questions to find their own answers.

Oceanflavored, let's start out with the basics so we can assess where you're getting stuck.

So, first explain to us in your words what a resonance structure is (yes, we know, I want to know if you know).

Second, when you write PO4 (3-), what does the 3- signify?

Third, you put a note that your Lewis structure is "messed up," and indeed it is, but in order for us to know what you do and don't know, we need to know what part of the Lewis structure YOU think is messed up. So since you haven't been able to type it out, can you describe to us in words what you are starting with? Start with the P and then describe where the 4 oxygens are relative to that and how many bonds you are assigning for each position. For the sake of clarity, you can use terms such as up, down, left, right, or north, south, east, west...whatever helps tells us what direction you are drawing bonds sticking out of each atom in your diagram.

Lastly, as you draw the Lewis structure, remember to put the dots on it for where the electrons are.

We will wait for your next response before continuing forward, because I suspect I see where you're running into difficulty, but need to confirm it and figure out why you're stuck there before helping you figure this one out.

1. What is the chemical formula for PO4 (3-)?

The chemical formula for PO4 (3-) is a polyatomic ion that consists of one phosphorus atom and four oxygen atoms, with a charge of -3.

2. How many resonance structures does PO4 (3-) have?

PO4 (3-) has three resonance structures, which can be drawn by moving the double bonds between the phosphorus and oxygen atoms in different arrangements.

3. Why are resonance structures important for PO4 (3-)?

Resonance structures are important for PO4 (3-) because they help to explain the delocalization of electrons in the molecule, which affects its stability and reactivity.

4. How do you determine the major resonance structure for PO4 (3-)?

The major resonance structure for PO4 (3-) is determined by following the rules of resonance, which state that the structure with the lowest formal charges and the greatest number of covalent bonds is the most stable.

5. What is the overall charge of PO4 (3-)?

The overall charge of PO4 (3-) is -3, due to the three extra electrons from the negative charge on the polyatomic ion.