The structural parameters and vibrational frequencies are predicted for the cycloalkanes C.H2• and silacycloalkanes SiC,_1H2n, n = 3-6, using the 3-21G* basis set and SCF wave functions. Bent bond lengths are predicted by tracing the paths of maximum electron density connecting atomic centers. Strain energies and heats of formation are predicted for these compounds and some smaller acyclic alkylsilanes by using MP2/6-31G(d) energies at the 3-21G* geometries and the appropriate homodesmic reactions.