What are the criteria for classifying compounds as ionic?

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Discussion Overview

The discussion revolves around the criteria for classifying compounds as ionic, with participants examining specific examples and seeking to understand the general principles that govern ionic classification. The scope includes theoretical considerations and practical examples from chemistry.

Discussion Character

  • Homework-related
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants propose that MgCl2 and K2O are likely candidates for ionic classification, while others suggest HOCN and NH4NO3 might also be classified as ionic.
  • One participant notes that for binary compounds, a large difference in electronegativity is a criterion for ionic classification, while for more complex compounds, many salts are considered ionic.
  • A participant questions the existence of Li2, expressing uncertainty about its classification and existence in the laboratory.
  • Another participant acknowledges the existence of diatomic molecules like Li2, Na2, and K2 in gaseous phases, though they caution that this may not directly relate to ionic classification.
  • One participant raises a point about HOCN being expressible as ions (H+ and OCN-), questioning if this qualifies it as an ionic compound despite the covalent bonding of individual atoms.
  • Another participant counters that dissociation into ions does not necessarily imply ionic character, using gaseous HCl as an example of a covalent compound that can dissociate.

Areas of Agreement / Disagreement

Participants express differing views on the classification of specific compounds as ionic, and there is no consensus on the criteria for recognizing ionic compounds. The discussion remains unresolved regarding the classification of certain examples.

Contextual Notes

Participants discuss the complexity of ionic classification, highlighting the role of electronegativity and the nature of bonding in compounds. There are unresolved questions about the existence and classification of certain compounds, as well as the implications of dissociation in determining ionic character.

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Homework Statement



Which of the following compounds are properly classified as ionic? (select all that apply)
HOCN
SF4
NH4NO3
MgCl2
K2O
Li2
NF3

Homework Equations



n/a

The Attempt at a Solution



My initial choices were MgCl2 & K2O ... however, since this was incorrect (it didn't tell me which were correct or incorrect - the entire problem was either correct or incorrect)... I'm guessing that HOCN and NH4NO3 might also classified as ionic.

If this is true, what is the general criteria for recognizing ionic compounds (if the compound has more than 2 types of atoms)?

Thanks!
 
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skierboy said:
I'm guessing that HOCN and NH4NO3 might also classified as ionic.

Second for sure, not so sure about the first one.

If this is true, what is the general criteria for recognizing ionic compounds

In the case of binary compounds - large difference in electronegativity. In the case of more complex compounds - almost all salts are ionic.
 
Li2?
Am I the only one who has never heard of that?

Is it something that can/does significantly exist in some laboratory in gas phase?
 
Last edited:
I believe I have seen not only Li2, but also Na2 and K2 reported in gaseous phase. But don't quote me, I can be wrong.

Edit:

K2 at webelements:

http://www.webelements.com/potassium/bond_enthalpies.html

Not exactly what we are talking about, but an obvious sign that there are many exotic diatomic molecules.
 
Last edited by a moderator:
On the same note as NH4NO3, I found that HOCN can be expressed as two different ions as well: H+ and OCN-. Does that make it an ionic compound then?

I'm confused because the individual atoms are covalently bonded...
 
Not necesarilly. Gaseous HCl is covalent, but it easily dissociates into two ions.
 

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