Xe has a lower ionization enthalpy than Ne. The valence electrons in Xe (n = 5) are much farther from the nucleus than those of Ne (n = 2) and much less tightly held by the nucleus. They are more willing to be shared than those in neon. Also xenon has empty 5d orbitals which can help to accommodate the bonding pairs of electrons, while neon has all the valence orbitals filled.
