Here's why:

* Xenon's (Xe) bonding capacity: Xenon is a noble gas, meaning it has a full outer shell of electrons and is generally unreactive. While it can form compounds, it does so only under specific conditions and with highly electronegative elements like fluorine and oxygen.

* Chlorine's (Cl) bonding behavior: Chlorine is a halogen, meaning it typically forms single bonds with other elements. It rarely forms more than one bond with a single atom.

The reason XeCl8 isn't possible is that:

* Size and stability: Xenon's atomic radius is relatively large, making it difficult to accommodate eight chlorine atoms around it.

* Charge density: Eight chlorine atoms would create a significant negative charge density around the central xenon atom, which would destabilize the molecule.

In conclusion, XeCl8 is a hypothetical compound that is unlikely to be formed based on the chemical properties of xenon and chlorine.