[gavindor]

I once heard that ionic bonds don't have a bond length.. (or aren't said to have a bond length). And just covalent bonds do.

But looking at Mercury I Chloride  https://en.wikipedia.org/wiki/Mercury(I)_chloride

(which I understand to be an ionic compound consisting of the  Cation , being the Mercurious Ion  Hg₂ which is a polyatomic ion , covalently bound together. And the anion Cl₂ which is two chloride anions).

(Though wikipedia doesn't mention anything about cation and anion, and it being ionic compound, I think it is?). (And the picture in the top right with all the atoms packed together is typical for a diagram of an ionic compound)

But The article says  "the Hg–Cl bond length in the linear Hg₂Cl₂ unit is 243 pm"

I don't really see if the connection between Hg and Cl, is a Covalent bond, and assuming it's not, then  i'm not sure why it mentions "bond length"?

[Hunter2]

All compounds with atoms have bond length.

https://www.quora.com/Do-ionic-compounds-have-bond-lengths-or-not

[gavindor]

All compounds with atoms have bond length.

https://www.quora.com/Do-ionic-compounds-have-bond-lengths-or-not

yeah that quora link suggests that for ionic compounds, it's called the "interatomic distance"  and for NaCl is also the edge of part of a unit cell. (which I can tell from a link mentioned by that quora answer).

I see these links speak of it too and witht different names

https://phys.libretexts.org/Bookshelves/University_Physics/Book%3A_University_Physics_(OpenStax)/University_Physics_III_-_Optics_and_Modern_Physics_(OpenStax)/09%3A_Condensed_Matter_Physics/9.02%3A_Types_of_Molecular_Bonds 

"The equilibrium separation distance (or bond length) between the ions"


or http://pd.chem.ucl.ac.uk/pdnn/refine2/bonds.htm  mentions

"For ionic structures, one simply adds the appropriate pair of radii together in order to obtain an approximate interionic distance"

Thanks

[Corribus]

The ionic bond length would be the distance between two adjacent ionic nuclei. But the issue with strictly ionic compounds is that they form regular lattices instead of discrete molecules, so it can be difficult to identify which interactions should be considered the basis of a single "ionic bond". In particular, some lattices may have complicated cell shapes with different possible interatomic distances depending on which lattice points are selected. So does one take an average? Also, the same formula may have different polymorphs depending on how the crystal was formed, what impurities are present, and so forth, all of which can affect the crystalline cell dimensions and effective internuclear distances. In that sense, a question like, "what is the ionic bond length in calcium carbonate?" has no general answer and I would be wary of just grabbing values off the internet without knowing what they represent (some values aren't directly measured, they just add the radii of two ions measured in isolation and call that an ionic bond length between the two in whatever lattice they might appear in).