Recently emerging two‐dimensional (2D) bismuth, bismuthene, has excited the world scientific community. It has been successfully synthesized to show high structural stability. Bismuthene possesses enhanced interaction with gas molecules due to its large surface area, which is a characteristic feature of 2D materials. This work performs a systematic first‐principles study on the effects of the environmental gas molecules (CO, NO, NO2, H2, and NH3) on the electronic structure and chemical activity of bismuthene. It is found that CO, NO, and NO2 serve as charge acceptors. Furthermore, the adsorption of NO and NO2 can produce noticeable modifications in the band structure of bismuthene. H2 and NH3 act as charge donors to bismuthene. Importantly, there is a large amount of transferred charge and a low adsorption energy of H2 on bismuthene. Thereby, our study suggests bismuthene as a promising material for gas sensing applications and production of hydrogen storage devices. [ABSTRACT FROM AUTHOR]