[wpotr]

  :confused:I am making a bohr model of cobalt for my class.  When I check all sources, they say that there are 15 elec. in the third shell and 2 elec. in the forth shell.  I thought there were 8 elec. in the third shell and 9 elec. in the forth shell...can anyone help?

[nakada]

It is imposible for a 4th shell to have more electrones than the third, because if you look at energy level diagram you can see clearly that 4s, and 3d orbitales are on the same energy level, so the first orbitale that is filled with electrones is 4s (2 electrones), than 3d (10 e), than 4p (6 e), and so on!  

[nakada]

But don`t get me wrong, it would be wise to review all data about energy level diagram, and Hnd`s rule. Also you should understand that 4s orbitale is not first orbitale to be filled. You probably know that everything starts with 1s orbitale, than 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d..