 By contrast, in both the polysilicon dihalides and the polysilicon monohalides, as well as the polysilicon hydrides, the silicon atom is tetravalent with a local coordination geometry that is tetrahedral, even though the stoichiometry of the monohalides ([Si"X"]n = SinXn) might erroneously imply a structural analogy between perhalopolysilynes and [linear] polyacetylenes with the similar formula (C2H2)n. The carbon atoms in the polyacetylene polymer are sp2-hybridized and thus have a local coordination geometry that is trigonal planar.However, this is not observed in the polysilicon halides or hydrides because the Si=Si double bond in disilene compounds are much more reactive than C=C double bonds.Only when the substituent groups on silicon are very large are disilene compounds kinetically non-labile.