[XxslbabesxX]

This may be a silly question, but I was wondering why, for example, Cr₂O₆ has to be reduce to CrO₃ (according to my teacher), but for something like Octane, C₈H₁₈, it does not reduce to C₄H₉.

[Yggdrasil]

It has to do with whether the compound is ionic or covalent.  In ionic compounds, the formula represents the ratio of atoms in the crystaline solid.  There are no actual molecules of CrO₃.  Therefore, the empirical forumla is used.  However, in a covalently-bound compound, actual molecules do exist and these molecules consist of the exact number of atoms described in the molecular structure.

[XxslbabesxX]

Thank you for your help