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Is Formula Unit usually an empirical formula but not always?

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gavindor:
I know that a formula unit is what ionic compounds have. (i.e.  ionic compounds  being not composed of molecules). And I know that the term empirical formula can apply to molecular formulae or to formula units.

Is Formula Unit usually an empirical formula but not always an empirical formula?

e.g. common examples are ionic compounds NaCl and CaCO3  but from what I understand there are also examples of ionic compounds whose formula unit is not an empirical formula , i.e. the ratio of atoms in the formula are not in their simplest form , for example Hg2N2O6 https://pubchem.ncbi.nlm.nih.gov/compound/129646128   or K2S2O8 https://en.wikipedia.org/wiki/Potassium_persulfate  Their empirical formulae would be HgNO3 and KSO4 respectively.

Hunter2:
Can KSO4 exist? No some bonding missing. HgNO3 theroretical can exist. But mercury-I connect two Hg in there molecules. So it would be Hg2(NO3)2 or Hg2N2O6

Borek:

--- Quote from: gavindor on October 05, 2023, 01:21:57 AM ---Is Formula Unit usually an empirical formula but not always an empirical formula?
--- End quote ---

Yes.

Also Hg2Cl2.

gavindor:

--- Quote from: Hunter2 on October 05, 2023, 03:06:32 AM ---Can KSO4 exist? No some bonding missing. HgNO3 theroretical can exist. But mercury-I connect two Hg in there molecules. So it would be Hg2(NO3)2 or Hg2N2O6

--- End quote ---

KSO4 and HgNO3 are empirical formulae. So I think they don't have to exist?

The Formula Units exist Hg2N2O6  and K2S2O8

Hunter2:
That is what I am saying.

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