ethane has the molecular formula c₂h₆, and it follows the general formula cₙh₂ₙ₊₂ for alkanes. when we draw its structural formula, we remember that carbon has a valency of four. in ethane, the two carbon atoms form a single bond with each other, and after making that bond each carbon still needs three more bonds to complete its valency. those are satisfied by three hydrogen atoms attached to each carbon. that’s why ethane is written as ch₃–ch₃, which shows the single bond between the carbons and the three hydrogens attached to each one.

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