Bohr's planetary model ofatom There are only a limited number of permitted Photon energy levels in an atom and an electron can only stay in these energy levels Each energy level has a n principal number n(主量子数) The energy level with n=1 has the lowest energy 3Bohr’s planetary model of atom There are only a limited number of permitted energy levels in an atom, and an electron can only stay in these energy levels. Each energy level has a principal quantum number n (主 量子数). The energy level with n=1 has the lowest energy