Density functional calculations for both periodic slabs and different size cluster models of the hydrogen-terminated (100) Surface of silicon are used to Study a new configuration, formed by a silylene center interacting with vicinal silicon dihydrides through nonconventional hydrogen bonds. A comparison between slab-model and cluster-model approaches to modeling Surface silylene defect formation processes is presented. The cluster models are used to analyze the structure and bonding of the silylene with a Lewis acid and base, showing the Zwitterionic nature of the defect. The silylene is also demonstrated to behave as a strong Bronsted acid. The stabilization of the silylene defect via interaction with species unavoidably present in the HFaq-etching solution is investigated. Finally, the negative chemical shift observed by X-ray photoelectron spectroscopy in the HFaq-etched (100) Si Surface is attributed to the occurrence of silylene defect.