# What are Polyatomic ions

1. Nov 6, 2005

### scott_alexsk

What are the monoatomic ions or elements( I am not sure anymore) that make up carbonate? Once this is answered I can ask my real question.
-Scott

2. Nov 7, 2005

### mrjeffy321

Carbonate is CO3 with a -2 charge on the ion.

3. Nov 7, 2005

### scott_alexsk

Knowing what monoatomic ions that make up the carbonate allows me to settle a dispute I have had with several people. Orginally my teacher said that the atoms making up the carbonate were all neutral. I had a feeling they were monoatomic ions involved. Now that I know this do monoatomic ions occur naturally in nature and if so how do they occur and are they stable? I mean how would carbonate come to be. From what elements would oxygen be able to take a single electron, then in another reaction bond with carbon?
Thanks for your help so far.
-Scott (Hey who deleted that last guys post that I just responded to?)

4. Nov 7, 2005

### mrjeffy321

the atoms making up the Carbonare ion (Carbon and 3 Oxygens), are not necesarily held together ionicly. The Ion as a whole has a charge, but the individual components of the ion can be held together covalently by sharing electrons.

Monoatomic ions can occur however.
Quite often in the alkili or alkiline earth elements will form cations (+), and the halogens and the "chalcogens" (I think that is their name) will form -2 charges. Transition metals can form all sorts of different charges.
Take this compound for instance,
Iron (III) Oxide, Fe2O3,
the Iron has a +3 charge, the Oxygen has a -2.
or Sodium Chloride, NaCl
Sodium has a +1 charge, Chlorine has a -1 charge.
Or in [acidic] water, the Hydronium ion will form, which can be written as H3O+1 or H+

5. Nov 7, 2005

### Gokul43201

Staff Emeritus
Even covalent bonds have some polarity (or ionic character) and hence there can be partial charge held by different atoms of the radical. In the carbonate radical, most of the 2- charge is held by two of the three O-atoms (the two that are single-bonded to the C-atom.

6. Nov 7, 2005

### ShawnD

Carbonate is actually a resonsance structure. If you draw a lewis structure, you would have it so one of the oxygens is double bonded, and two the oxygens are single bonded and able to make one bond each. The lewis structure does the job for all intents and purposes, but it's technically incorrect. The charge isn't held by any specific oxygen(s), but it's shared among the three of them.
I would conclude that monoatomic ions are not involved, but that's just my opinion.

As for the monoatomic ions and their stability, no they do not exist. You'll never find carbon with a +4 charge as an ion; that just won't happen. You also won't find oxygen as 2-. All metal oxides are bases as soon as they touch water, and all nonmetal oxides are acids when they touch water; remember that water is almost everywhere, even in the air.
CaO + H2O --> Ca(OH)2 the OH does not break apart, so the O isn't a standalone ion
CO2 + H2O --> H2CO3 the O's stay as part of the resonance structure of CO3, still no standalone O ions

Last edited: Nov 7, 2005
7. Nov 8, 2005

### scott_alexsk

There is the reason I asked the question in the first place. There has been such a contraversy over what the simple composing elements/ions that make up carbonate. With someone finally agreeing with what my chemistry teacher said, how can the bonded elements have a charge in this structure? I mean what allows bonded nuetral atoms to become not nuetral?
-Scott

8. Nov 8, 2005

### ShawnD

I'm not really sure I'm interpreting your question correctly but I'll try.

Ionic and covalent bonds are basically the same thing, but the terms themselves represent how things dissociate. Take something like NaCl. Na loses an electron, Cl gains an electron. The Na has a very weak attraction to the electrons, so it just accepts defeat and leaves the electrons to Cl. NaCl isn't even a molecule; it's just a ratio between atoms. Now look at something like CO2. O takes electrons from the C, but the C still holds onto those electrons; it's like a tug of war. Since the carbon and oxygen never really separate, you can't say that either has an official charge, but you can definitely say the oxygen is negative compared to the carbon because it can hold the electrons tighter than carbon can. Now throw that CO2 into water and you get H2CO3 (just slap a water on). H2CO3 does exist as a single molecule, but it has a dissociation constant tied to it. The hydrogens are bound to the oxygens, and as you know, oxygen has a much tighter grip on the elctrons than hydrogen does. Hydrogen just goes away without its electron leaving HCO3- and H+. This molecule also has a dissociation constant. Another hydrogen can leave, again without an electron because oxygen stole it, to get CO3-2 and another H+.
The negative charge is just there to show that the source of those electrons is no longer joined to the carbonate

9. Nov 8, 2005

### scott_alexsk

So as a result of the shared electrons within the polyatomic ions, the charge is not completely balanced and that produces a negative two charge in carbonate, right? I understand what you are saying about polarization within nuetral molocuels, but what makes these molocuels different than polyatomic ions which have a charge?
-Scott

10. Nov 8, 2005

### mrjeffy321

If you have neutral atoms coming together and bonding, no matter how disproportional the "share factor" is between them, the overall molecule will be neutral. However, in some cases, take Carbon Monoxide (CO) for instance, even though the overall molecule is neutral, the Oxygen develops a slight negative charge and the Carbon gets a slight positive charge due to the Oxygen pulling the electrons more towards its side of the molecule.
In some cases, one atom pulls so hard on the electrons of another atom, we say that it was completely removed from the original atom and added to the second atom. In this case, you have an ionic bond. So take Sodium (Na) and Chlorine (Cl), when these two react, the Chlorine takes an electron away from the Sodium to make Na+ and Cl-, which form an overall neutral ionic compound NaCl. Bonds can be considered partially covalent and partially ionic, since the electron is still technically shared between the two atoms by a certain percentage of the time.

The way a compound would get an overall charge is if it either gains or looses electrons to something else. For instance the Carbonate ion has a -2 charge; this is not because of any polarity in bonds inside the compound, but because it has an extra 2 electron.

11. Nov 8, 2005

### scott_alexsk

There is the problem. Some people like my chemistry teacher say that there are simply just elements making up these charged structures while others say that there are monoatomic ions making up the element. Repeatedly I have been told by reliable sources that the elements are perfectly neutral but to some structure unknown to me they can have a negative charge overall even though there are no additional electrons. Everyone here seems to have the same problem with answering this question.
-Scott

12. Nov 11, 2005

### Gokul43201

Staff Emeritus
The problem with this "discussion" is that the question really makes no sense to the responders and they are trying their best to interpret it in some manner that allows explanation. Scott, either you are wording your posts very poorly, or you are missing key concepts in your understanding.

It makes no sense at to say for instance "there are simply just elements making up these charged structures" or to say "there are monoatomic ions making up the element". This is just - to say it bluntly - gibberish.

You are confusing concepts like element, compound, molecule, atom, ion and radical. Please revise all these concepts, then go over the chapter that deals with Lewis structures. That should clear up any confusion you have.

This may be news to you, but there is NO controversy. It's possible that your chemistry teacher has a poor understanding of the concepts as well, but that's as far any controversy here goes.

Last edited: Nov 11, 2005
13. Nov 12, 2005

### scott_alexsk

That was very stupid of me. I apologize for wasting your time. Nevertheless it seems that there is a contradiction Gukul. ShawnD, my Chemistry teacher, and a college student I talked to all say that monatomic ions are not involved in the structure of the polyatomic ion carbonate. My chemistry teacher atleast said that the way the electrons are bonded allows for a prevailing negative charge because of the way the electrons are postioned in the bond. My orginal question was intended to try to understand what reasoning there is behind their answer but I got tied up in the red tape of the compostite radicals or elements of carbonate. I might as well ask what a resonance structure is because that might have something to do with it and may help in my understanding of the problem.
-Scott

14. Nov 12, 2005

### bomba923

As Gokul suggested, it might be a good idea to review your Lewis dot diagrams

Anyway, on with resonance:
Let's take carbonate as an example. To represent its structure--i.e., one of three major resonance forms---you would draw one carbon atom surrounded by three atoms of oxygen. (As it stands, a carbonate molecule $$\text{CO}_3 \, ^{2-}$$ is comprised of one atom of carbon along with three atoms of oxygen)

As you know, carbon is most likely (unless you deal with carbocations and carboanions, like I did when I took Organic Chemistry ) to have a neutral formal charge--->i.e., a formal charge of zero. (You can review formal charge http://www.westga.edu/~chem/courses/chem1212slattery/contents/chapter8-all/img031.gif [Broken]. It will help you construct your Lewis dot diagrams.)

Also, as you know, carbon has four valence electrons, and does not generally have lone pairs. Therefore, for the formal carbon charge to be zero, it must share 8 electrons.

However, carbonate is $$\text{CO}_3 \, ^{2-}$$, and therefore the atom of carbon must share 8 electrons with 3 oxygen atoms. What this means: two electrons will remain delocalized!

You see, no oxygen atom has a "specific priority" over the other oxygen atoms to receive these two electrons. Thus, you cannot form a localized double-bond. Those two delocalized electrons can exist any carbon-oxygen bond in carbonate!

And thus, we can draw three major resonance forms----->constantly transferring the "double bond" to a different oxygen each time we draw another such resonance structure.

And, due to those two delocalized electrons, we have an overall -2 charge for the carbonate molecule. Hence the term, "polyatomic" ion. Basically, you have carbonate anion.
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While carbonate has an overall -2 charge, oxygen is much more electronegative than carbon. Therefore, you will find that the two delocalized electrons will primarily/mainly exist around the oxygen atoms---->to give any two of the oxygen atoms a $$(\delta ^{-} )$$|->i.e., a partial negative.

You see, the carbon--oxygen bond is "polar covalent". While oxygen is more electronegative than carbon, the relative difference in electronegativity is too small to be pronounced "ionic". However, each major resonance structure will show two oxygens with an additional electron--->therefore, you might observe the oxygen atoms to possess -1 charge each. (Two of these oxygen anions will develop the overall -2 charge for the carbonate molecule).

Thus, we might say carbonate has two monoatomic oxygen ions in each of its distinct major resonance forms.

However, as ShawnD and I pointed out earlier, no oxygen or group of oxygens has a "specific priority" over the two delocalized electrons. Thus, no major resonance form will have a "specific priority" over the other major resonance forms.

Hope this helps!

Last edited by a moderator: May 2, 2017
15. Nov 13, 2005

### scott_alexsk

I really appreciate that and I think I get it. So even though the atoms making up the element are nuetral because of the dislocalization of the double bond, the prevailing outside charge is -2. Now I think I understand this, but why should the electrons cause a prevailng -2 charge? I mean how does the postion of the double bond electrons with all three oxygens create this charge? How are they postioned to escape the postive charge of the protons? Also is this true with all double bonds in nature (ie similar situation, different atoms)?

16. Nov 14, 2005

### LordOfBaal

You must see that the atoms can't be both charged and neutral at the same time. The carbonate ion is charged due to it having 2 extra electrons - no amount of double bond moving will remove this charge.

The part I think you are missing is -This polyatomic ion has picked up 2 electrons from the breaking of two bonds in which 2 +ve ions were released and the electrons from the bonds were wholly retained on the oxygen’s.

Resonance will probably only confuse the problem but with this ion we would use resonance to show that there are more than one ways of arranging the -ve charges, this has more to do with ion stability and structure than trying to understand overall charge.

There is a conservation of charge law that needs to be obeyed - No matter how exotic your resonance form looks or how much you move a double bond around if you start with a -2 charged molecule you must end up with a -2 charged molecule; if you don’t a chemical reaction has occurred.

Resonance is a tricky thing which you should not rush into untill you need to.:surprised

Hope I helped

Last edited: Nov 14, 2005
17. Nov 15, 2005

### scott_alexsk

I thought that the first explaination sounded werid anyways. So how does the carbonate get the -2 charge? Is it that there are monoatomic ions making up carbonate, if so which, or does it gain electrons from a different source?
-Scott

18. Nov 15, 2005

### bomba923

Conservation of charge, how's that difficult to understand?

Last edited: Nov 15, 2005
19. Nov 15, 2005

### ShawnD

If the ions were monoatomic, they wouldn't be polyatomic. Carbonate is polyatomic

20. Nov 17, 2005

### scott_alexsk

"I would conclude that monoatomic ions are not involved, but that's just my opinion."-ShawnD
Now that I am certain that carbonate has 2 more electrons than protons, hence the negative two charge, in what way does it obtain these electrons? Is it that it forms bonds with two monoatomic oxygen ions with a negative 1 charge, each, or is it something else as ShawnD suggests. How would carbonate gain electrons in your opinion? It is clear to me that it cannot simply just magically take electrons from another atom and remain unbonded, if Gukul and the others are incorrect, how do you justify your prior response ShawnD? I should have made myself more clear my prior post.
-Scott