title: Difluorosilane
text: # Difluorosilane
  
  Difluorosilane is a gaseous chemical compound with formula $SiH_2F_2.$ It can be considered as a derivative of silane with two hydrogen atoms replaced with fluorine.
  
  ## Production
  
  Difluorosilane can be made by fluorinating dichlorosilane with antimony trifluoride.
  
      3 $SiH_2Cl_2$ + 2 $SbF_3$ → 3 $SiH_2F_2$ + 2 $SbCl_3$
  
  Some is also made in a reaction of silicon tetrafluoride with hydrogen
  
      $SiF_4$ + 2 $H_2$ → $SiH_2F_2$ + 2 HF
  
  Traces of difluorosilane are made when coal is burnt.
  
  ## Properties
  
  Difluorosilane is a gas with boiling point −77.8 °C, and a freezing point of −122 °C. It has no colour. The silicon–fluorine bond length in difluorosilane is 1.358 Å which is greater than that in fluorosilane but less than the length in trifluorosilane.
  
  ## Reactions
  
  In an electric discharge, hydrogen atoms are preferentially removed from the molecule and $SiHF_2SiHF_2$ is formed along with hydrogen.
  
      2 $SiH_2F_2$ → $SiHF_2SiHF_2$ + $H_2$
  
  At elevated temperatures, difluorosilane can disproportionate by swapping hydrogen and fluorine atoms between molecules to form fluorosilane and trifluorosilane.
  
  ## Use
  
  Difluorosilane is used in dental varnish in order to prevent tooth cavities.
  
  Difluorosilane is also used in chemical vapour deposition to deposit silicon nitride films.
  
  