# Why don't molecules of ionic compounds exist?

My book says:

As single ions of a metal are not associated in the solid with single ions of a non metal, separate units of ionic compounds do not exist. It is, therefore, wrong to talk of a molecule of an ionic compound.

I know ionic solids exist in form of crystal lattice but why can't we isolate a single molecule of ionic compound?

• Actually compounds considered ionic in solid state are molecular in gas phase. Aug 8 '15 at 17:56

Quaternized glycine, $\ce{^{+}N(CH3)3-CH2-C(=O)O^{-}}$, is betaine. It is ionic, but the ions are covalently bound into a molecule. Where are the discrete formula units in alumina? You can draw lines to connect closest atoms, but those are not bonds. (Note fractional atom counts for atoms embedded in planes, edges, and corners.)
• How is this unit cell $\ce{Al2O3}$? It seems to have six aluminum and six oxygen atoms. Nov 21 '17 at 22:31