This paper presents a systematic investigation of chemical bonding in a series of noble-gas halides in both the gas phase and the solid state. The crystalline environment was simulated by a cutoff type Madelung potential. Geometries, dissociation energies, force constants, and enthalpies of formation and of sublimation were determined. The calculated properties are in good agreement with available experimental data. The crystal field model is capable of reproducing all significant differences observed between the gas phase and the solid state. KrF4, XeCl2 and XeBr2 are predicted to be rather unstable against molecular dissociation. The stabilities of the dihalides follow the order KrF2 much less than XeF2 < RnF2 and XeF2 much greater than XeCl2 approximate to XeBr2. The calculated trends account for the fact that only the heavier noble gases form compounds and that the electronegativity of the ligand has to be large. The outer polarization orbitals play an important role in the bonding. Relativistic effects on the molecular properties are negligible.