I know calcium nitride is Ca3N2, but why doesn't CaN2 exist (or at least not that I can find)?
Does not follow.The answer always lies in stability and energy (free Gibbs energy to be exact).
Taking into account fact metallic Ca can be safely kept under nitrogen, the answer is obviously "no" - even if you will manage to produce such a compound it will happily decompose into a stable mixture.
This confuses thermodynamics with kinetics. You can mix 2 mol hydrogen and 1 mol oxygen at room temperature even though 1 mol water is far more stable than the H2/O2 mix, from a thermodynamic (Gibbs energy) perspective. The reason is because the kinetics--the reaction of hydrogen and oxygen at room temperature--is extremely slow. CaN2 ends up being the same situation: a kinetic barrier prevents the decomposition of the compound into its constituents (although in this case, the kinetic barrier is likely far lower than in the case of the hydrogen-oxygen mixture).Taking into account fact metallic Ca can be safely kept under nitrogen, the answer is obviously "no" - even if you will manage to produce such a compound it will happily decompose into a stable mixture.
CaN2 (Ca[N2]) Crystal Structure
1.) I don't have an account with this website so I can't see the structure.
What do the [brackets] around N2 mean? Does this represent a double covalent bond between the nitrogen atoms in comparison with an ionic bond between Ca and N2?
2.) Is it also possible for HK[N2] to exist as well? By this I mean two nitrogen atoms with a double covalent bond and then both a hydrogen atom and a potassium atom forming ionic bonds with the nitrogen atoms. Or will this compound break down into N2 + HK (potassium hydride)?
I'm not sure why but I can't see the structure with that article either. Maybe you have to be logged in as well, or maybe I have no idea what I'm doing. Anyway, I think I know what it looks like. Thanks againGreetings,
The reference provided by @TeethWhitener shows the crystal structure. I assume that the bracket notation indicates that the nitrogen is structurally N2 as opposed to two N's. But that is an assumption although one consistent with the crystal structure.
As for HK[N2], I do not know. The only results I get on Google are to a Hong Kong flu virus.
OK but the intuition you supplied in post 4 was incorrect. @snorkack gave a better way of thinking about it in post 5 and I pointed out the classic freshman disconnect between thermodynamics and kinetics that plagues beginner chemists. I don't really see anything wrong with how this thread's gone.IMHO you are doing the OP disservice reinforcing their misunderstandings of the basic concepts. Discussing exotic cases as if they were a standard and basic chemistry doesn't help to build a required intuition :(