Its like this bohr model is designed to determined the valence electron of the certain element. so, you will first determine the number of electrons of the certain element, *btw number of electrons is equall to its atomic number..... example Oxygen, the atomic number of this element is 8 which means it has also contains 8 electrons. then, you'll proceed in distributing the electrons. the first orbital contains 2electons then the second contains 6electrons so its valence is 6.. ANY FURTHER QUESTION?