# Why are the ozonides of heavier elements more stable?

The ozonides of $\ce{Cs}$, $\ce{Rb}$, $\ce{K}$ are well known and relatively stable, but there is little mention of the ozonides of $\ce{Na}$, $\ce{Li}$. Why is this?

• They are extremely unstable according to Wikipedia. You can sort of guess why- the ozonide ion is big for the tiny Sodium and Lithium ions so it is stretched around it due the distributed charge on the ozonide ion- puts it under large internal stresses. – user2617804 Nov 22 '14 at 7:19

Lithium and sodium ozonide are extremely unstable and must be prepared by low-temperature ion exchange starting from $\ce{CsO3}$. Sodium ozonide, $\ce{NaO3}$, which is prone to decomposition into $\ce{NaOH}$ and $\ce{NaO2}$, was previously thought to be impossible to obtain in pure form. However, with the help of cryptands and methylamine, pure $\ce{NaO3}$ may be obtained as red crystals isostructural to $\ce{NaNO2}$.