What are the criteria for classifying compounds as ionic?

[skierboy]

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!

 

[Borek]

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.

 

[epenguin]

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?

 

[Borek]

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.

 

[skierboy]

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...

 

[Borek]

Not necesarilly. Gaseous HCl is covalent, but it easily dissociates into two ions.