How many electrons are in the outermost energy level of an oxygen atom?
There is a pattern to the periodic table based on the number of electrons in the sublevels. (Sublevels are part of the energy levels). I can't describe all the details of the pattern now but here is a brief description.
Column 1 = 1 outer electron
Column 2 = 2 outer electrons
Column13 = 3 outer electrons
Column 14 = 4 outer electrons
Column 15 = 5 outer electrons
Column 16 = 6 outer electrons
Column 17 = 7 outer electrons
Column 18 = 8 outer electrons (except He)
The maximum outer electrons that an element will have is 8 but that is getting into an area that is more complicated. That doesn't mean 8 total electrons, only 8 outer electrons.