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Protonated methane, CH5, is a key reactive intermediate in hydrocarbon chemistry and a borderline case for chemical structure theory, being the simplest example of hypercoordinated carbon. Early quantum mechanical calculations predicted that the properties of this species could not be associated with only one structure, because it presents serious limitations of the Born−Oppenheimer approximation. However, ab initio molecular dynamics and diffusion Monte Carlo calculations showed that the most populated structure could be pictured as a CH3tripod linked to a H2moiety. Despite this controversy, a model for the chemical bonds involved in this ion still lacks. Here we present a modern valence bond model for the electronic structure of CH5. The chemical bond scheme derived directly from our calculations pictures this ion as H3C···H2. The fluxionality can be seen as the result of a proton transfer between C−H bonds. A new insight on the vibrational bands at ∼2400 and ∼2700 cm-1is suggested. Our results show that the chemical bond model can be profitably applied to such intriguing systems. [ABSTRACT FROM AUTHOR]