This work is dedicated to obtaining new data on the adsorption properties of silicon in nanowire (NW) geometry for application in sensors. It has been experimentally shown that silicon without modification can be used for selective  detection of ammonia and hydrochloric acid. Quantum chemistry modeling indicates that during the adsorption of NH3, HCl, and H2O molecules, the electron density redistributes between the adsorbate and the silicon surface,  leading to changes in electrical conductivity of the silicon sample. A model linking the change in the conductivity of the silicon sample with the time during which it is exposed to analyte vapor has been developed. The effective  sticking coefficient for water adsorption on the silicon NW surface was estimated from experimental results and quantum chemical calculations.