The atomic structure and energetics of the clean (100)-(2 X 1), (100)-(2 X 1):H monohydride, (100)-(1 X 1):2H full dihydride, (100)-(3 X 1):1.33H intermediate dihydride, and other intermediate hydride surfaces obtained by local removal of H atoms from or addition of H atoms to the (2 X 1) monohydride, are investigated by molecular mechanics (MM3). The monohydride phase is found to be the most stable thermodynamically and is predicted to be the dominant phase under chemical vapor deposition conditions. Gas-surface reactions relevant to diamond chemical vapor deposition involving hydrogen and the diamond (100)-(2 X 1):H surface are discussed in light of the derived energetics.