"Molecular ions"

[Amaton]

What exactly is a molecular ion? I ask because there appears to be nothing obvious that distinguishes a molecular ion from a polyatomic ion. I would be satisfied with personal inference but that merits nothing in regards to the correct and rigorous classification. I'm not sure if there's actually a subtle difference or if the terms are synonymous and thus interchangeable (the Wikipedia page seems to support the latter notion).

 

If there is a distinction, I suspect it has to do with the type of bonding involved. Just looking for someone to shed light on these two terms. Thanks in advanced

[CaptainPanic]

To be honest, I am not entirely sure. I would agree that in most cases, the terms two are the same. Perhaps if you have an ion and you also consider its ligands, this is considered a polyatomic ion, but it is not a single molecule, therefore not a molecular ion??

 

Perhaps some of our chemistry experts can shine a light on this. My chemical engineering background is not enough to answer your question. Until you get a better answer than mine, I would consider the two terms the same.

[Enthalpy]

http://www.britannica.com/EBchecked/topic/388166/molecular-ion

looks like the same notion used by a different profession. Let's see what chemists say to that.

[Amaton]

To be honest, I am not entirely sure. I would agree that in most cases, the terms two are the same. Perhaps if you have an ion and you also consider its ligands, this is considered a polyatomic ion, but it is not a single molecule, therefore not a molecular ion??

 

Thanks. That certainly could be.

 

With a quick search, I encountered a certain answer, a rather funny one, because it is from Yahoo!Answers. However, the contributor seemed knowledgeable in chemistry as per his other answers and established ranking (but this is a personal first for trusting Y!A). The question page is here.

 

I'm surprised I have yet to find anything that explains either or their distinction from an authoritative organization.

 

 

 

http://www.britannic...6/molecular-ion

looks like the same notion used by a different profession. Let's see what chemists say to that.

 

I took greater notice to the latter excerpt, "The electron beam generates, among other things, a positively charged molecule known as a

molecular ion, which results from the removal of one electron from the molecule."

 

It seems one can think of it as where the ion is derived from (?), i.e. molecular ions derive from molecular structures and thus molecular ions are a subset of polyatomic ions.

[hypervalent_iodine]

Molecular ion is usually a term encountered when looking at mass spec and is as Amaton described, though it's also worth noting that molecular ions are radical cations. I have not seen it used in other contexts. Polyatomic ions describe species such as CO₃^2- and NO₃^-, which are ions because of their charged nature and polyatomic because they are comprised of more than one type of element. You would not use the term polyatomic ion in the same context as molecular ion.

[Amaton]

Molecular ion is usually a term encountered when looking at mass spec and is as Amaton described, though it's also worth noting that molecular ions are radical cations. I have not seen it used in other contexts. Polyatomic ions describe species such as CO₃^2- and NO₃^-, which are ions because of their charged nature and polyatomic because they are comprised of more than one type of element. You would not use the term polyatomic ion in the same context as molecular ion.

 

Ah. So it basically comes down to whether or not the ion has unpaired valence electrons? Or is there more to it?

[hypervalent_iodine]

What I was describing was more a difference in context. I suppose the names are fairly interchangeble if you are not talking about mass spec. You could call a polyatomic ion a molecular ion and be correct - the names would indicate that they are the same thing, since nitrate and carbonate, etc., are molecules.

[Amaton]

What I was describing was more a difference in context. I suppose the names are fairly interchangeble if you are not talking about mass spec. You could call a polyatomic ion a molecular ion and be correct - the names would indicate that they are the same thing, since nitrate and carbonate, etc., are molecules.

 

That makes sense. So an example of a polyatomic ion that is not a molecular ion would be, say, a coordination complex?

[hypervalent_iodine]

That makes sense. So an example of a polyatomic ion that is not a molecular ion would be, say, a coordination complex?

 

 

No, I think you have misunderstood me or I am not being very clear. I mean to say that you could call all polyatomic ions molecular ions. There is no difference in that sense, but the term molecular ion is also used to refer to something in mass spectrometry that you would not use the term polyatomic ion for.

[Amaton]

No, I think you have misunderstood me or I am not being very clear. I mean to say that you could call all polyatomic ions molecular ions. There is no difference in that sense, but the term molecular ion is also used to refer to something in mass spectrometry that you would not use the term polyatomic ion for.

 

Okay, my apologies. Your explanations were fine. My mind just kept bringing up other potential discrepencies aside from what you were saying. I realized they were irrelevant though, so it's all good I suppose.