Why does PbCl4 exist but PbIO4 doesn't?

PbCl₄ exists because a Pb atom has four .

The of Pb is [Xe] 6s²4f¹⁴5d¹⁰6p².

The inner subshells are filled, so the are 6s²6p².

The most common oxidation state of Pb is +2, formed by the loss of the 6p electrons.

The less stable oxidation state of Pb is +4, formed by the loss of the 6p and the 6s electrons.

So PbCl₄ can exist, but it is somewhat unstable.

In PbIO₄, the periodate ion (IO₄⁻) has a charge of -1. So Pb would have a charge of +1.

Pb would have to lose just one 6p electron.

It can achieve a more stable state by losing two 6p electrons and getting down to a filled 6s subshell.

If lead periodate exists, it will probably have the formula Pb(IO₄)₂.