# Structure of chromium trioxide

According to most sources, $\ce{CrO3}$ has the following Lewis structure (courtesy ChemSpider):

However, it is also not planar (courtesy Wikipedia):

Implying that there is a lone pair somewhere.

1. What is the electron configuration of the $\ce{Cr}$ atom?
2. Which orbital is responsible for the three double bonds?
3. Where does the lone pair come from?
4. How would its MO diagram look like?