  The stability of Ne@C$_{60}$ and He@C$_{60}$ is discussed in the context of a
spherical model where the carbon atoms are smeared out into a uniform shell.
The electronic properties of the sixty $\pi$ electrons together with those of
the central atom are treated in the Thomas-Fermi approximation. Simple
electrostatic reasoning elucidates the nature of the radial stability of the
complex. A method to include non-spherical corrections is outlined. Possible
bonding topologies of the central atom and the C$_{60}$ cage are discussed, as
well as the relevance of these topologies to incipient central atom
distortions.

Chemical Physics;Atomic Physics;Condensed Matter;Materials Science;Chemical Physics