Questions about polyatomic ion compounds

In summary: But how would it get one? Would the Na pull an electron from the Nitrate?Sorry for my denseness, by the way!In summary, the conversation discusses confusion about polyatomic ions, specifically in regards to how they gain charges and form acids. The expert explains that nomenclature may be causing confusion and clarifies that both covalent and ionic compounds are neutral when seen from the outside, but the charge is not evenly distributed within the molecule. The expert also explains how acids are formed and how ionic compounds with polyatomic ions work. The conversation ends with the individual still feeling unsure about polyatomic ionic compounds.
  • #1
Ser
8
0
I'm extremely confused in regards to many aspects concerning polyatomic ions. For one, am I correct in thinking that covalent polyatomic ions gain charges by having components dissociated? Ex. A and B are sharing an electron, A has a significantly greater hold, B is dissociated by something leaving A with the electron and the compound now having a - charge?

If my understanding of that is correct, here are some questions about polyatomic ion compounds:
1) Acids are covalent, right? Well how do they form, then? The polyatomic ion dissociates H+(s) from other compounds?
2) Well how does, say, Hydrobromic acid form? How can, in a covalent bond, an H+ and Br- come together? That seems ionic...they both dissociated from something else and happened to come together covalently but the electronegativity is even enough that the partial charge isn't significant so the + and - parts balance the charge?
3) Finally, how do ionic compounds with polyatomic ions work? If, say, Nitrate pulls off an electron from a group 1 element that element is now +1 and Nitratre is -2...how does that balance?

So confused..thanks in advance for bearing with my questions. I'm undoubtedly missing something here.
 
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  • #2
Ser said:
I'm extremely confused in regards to many aspects concerning polyatomic ions. For one, am I correct in thinking that covalent polyatomic ions gain charges by having components dissociated? Ex. A and B are sharing an electron, A has a significantly greater hold, B is dissociated by something leaving A with the electron and the compound now having a - charge?

This is more or less correct, although nomenclature you use - "dissociated by something" - doesn't make sense to me. Just dissociated.

1) Acids are covalent, right? Well how do they form, then? The polyatomic ion dissociates H+(s) from other compounds?

No idea what you are asking, this is again nomenclature problem. However, you may assume that some bonds are ionic while others are covalent in the same molecule.

2) Well how does, say, Hydrobromic acid form? How can, in a covalent bond, an H+ and Br- come together? That seems ionic...they both dissociated from something else and happened to come together covalently but the electronegativity is even enough that the partial charge isn't significant so the + and - parts balance the charge?

HX (where X is any halogen) are a little bit tricky. The molecule - in tha gas phase - is covalet. However, when it gets dissolved, it dissociates because both cation and anion are solvated by water molecules, and they are much more stable in water as solvated ions,. than as covalent molecule.

3) Finally, how do ionic compounds with polyatomic ions work? If, say, Nitrate pulls off an electron from a group 1 element that element is now +1 and Nitratre is -2...how does that balance?

Nitrate doesn't pull electron. If anything, reaction goes like

2Na + 2H+ -> 2Na+ + H2

and nitrate doesn't change in the reaction. Reality is a little bit more complicated, as sodium is very reactive and it will not "wait" for H+, it will react directly with water, but that's the general idea.
 
  • #3
Borek said:
No idea what you are asking, this is again nomenclature problem. However, you may assume that some bonds are ionic while others are covalent in the same molecule.

What I meant is that since the polyatomic ions have negative charges, how do they covalently bond with hydrogen to become neutral? The hydrogens would have to be already be cations when they bond?

With the Nitrate question I was referring to the Nitrate polyatomic ion NO3-1. When it forms an ionic bond it's pulling off electrons, right? Well I can understand ionic bonds with elements perfectly but here it looks like Nitrate pulls off an electron, giving it an additional negative charge, and the other thing yields its electron, giving that a positive charge. The negative and positive cross out but the original -1 charge seems like it's still there, regardless of how many it pulls? With, say, potassium and fluoride the fluoride pulls one, K is +, F is -, even. But with, for example, Nitrate if it goes into an ionic bond and pulls electrons from something like K (just as a random example) the charge will stay "evened out" like with K and F but the -1 will still be there. How is that removed?

Also, with your explanation of Hydrobromic acid, does that mean that the hydrogen and bromide are neutral until they get dissociated?

Thanks :)
 
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  • #4
Ser said:
What I meant is that since the polyatomic ions have negative charges, how do they covalently bond with hydrogen to become neutral? The hydrogens would have to be already be cations when they bond?

Could be that's thing that you are missing here. Both covalent and ionic compounds are neutral when seen from the outside. HCl molecule is neutral, HNO3 is neutral as well. However, charge INSIDE of the molecule doesn't have to be distributed evenly - one of electrons is moved from H to NO3, so they are already charged, although only partially. When making acid you synthesize NEUTRAL molecule in which charge is not distributed evenly, and when it dissociates, charge gets separated - H becomes H+, NO3 becomes NO3-. If - for any reason - they recombine - negatively charged anions reacts with positively charged cation, giving neutral molecule.
 
  • #5
Borek said:
so they are already charged, although only partially. When making acid you synthesize NEUTRAL molecule in which charge is not distributed evenly, and when it dissociates, charge gets separated - H becomes H+, NO3 becomes NO3-. If - for any reason - they recombine - negatively charged anions reacts with positively charged cation, giving neutral molecule.
I still seem to be missing something...My thought process is that Nitrate has a net -1 charge by itself. When you say they detach into H+ NO3- I guess that means the hydrogen was initially a cation before the nitric acid was formed? If so, I understand it now and my main confusion then would be polyatomic ionic compounds.

NO3- + Na, how would that work? Obviously you need a + to balance the overall molecule but how does that happen? If I'm correct, the sodium gives up an electron to the nitrate, which gives sodium a +. But that makes Nitrate -2, so it isn't balanced?
 
  • #6
Ser said:
I still seem to be missing something...My thought process is that Nitrate has a net -1 charge by itself.

Nitrate anion, not nitric acid nor - for example - sodium nitrate, which are neutral.

When you say they detach into H+ NO3- I guess that means the hydrogen was initially a cation before the nitric acid was formed?

Depends on what do you mean by "before the nitric acid was formed". If we assume you make nitric acid dissolving dinitrogen pentoxide in water:

N2O5 + H2O -> 2HNO3

you start with neutral molecules and you end with neutral molecules. Charges appear during dissociation:

HNO3 -> H+ + NO3-

NO3- + Na, how would that work? Obviously you need a + to balance the overall molecule but how does that happen? If I'm correct, the sodium gives up an electron to the nitrate, which gives sodium a +. But that makes Nitrate -2, so it isn't balanced?

No, it is not NO3- + Na, it is already NO3- + Na+. Why do you think you start with atomic sodium and NO3-? To synthesize sodium nitrate you have to either start with nitric acid and metallic sodium (in which case sodium will react with H+ from acid dissociation, NO3- is untouched) or with - for example - sodium hydroxide - in which case sodium is already in the cationic form (and NO3- is untouched again).
 
  • #7
Borek said:
Why do you think you start with atomic sodium
Aha! I knew it was something dumb I was thinking. Now I understand that, too. Thanks for the help, much calmer in my head now that I get it.
 

Related to Questions about polyatomic ion compounds

1. What is a polyatomic ion?

A polyatomic ion is a charged molecule made up of two or more atoms that are covalently bonded. These ions have an overall charge due to the unequal distribution of electrons within the molecule.

2. How are polyatomic ions named?

Polyatomic ions are named based on their chemical composition and charge. The cation (positively charged ion) is usually named first, followed by the anion (negatively charged ion). The ending of the anion's name is often changed to -ite or -ate to indicate a lower or higher number of oxygen atoms, respectively.

3. What is the difference between a polyatomic ion and a monatomic ion?

A polyatomic ion is made up of two or more atoms, while a monatomic ion is made up of only one atom. Polyatomic ions have a net charge, while monatomic ions have a positive or negative charge.

4. How do you determine the formula for a compound with polyatomic ions?

To determine the formula for a compound with polyatomic ions, you need to first identify the ions present and their charges. Then, use the criss-cross method to determine the number of each ion needed to balance the charges. Finally, write the formula with the cation first and the anion second.

5. Can polyatomic ions form covalent bonds?

Yes, polyatomic ions can form covalent bonds with other atoms or ions. This is because they are already made up of covalent bonds between their constituent atoms. However, polyatomic ions can also form ionic bonds with oppositely charged ions.

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