Hydrogen and other 1 electron systems are the only ones accurately explained by the Bohr Model Problems with Bohr’s Model When there is more than one electron interactions between the nucleus and electrons become too complicated for the Bohr model. Other ions that also have one electron can also be explained accurately (for example, He +). When there is more than one electron the model does not accurately predict the energies. The Bohr model of hydrogen is the only one that accurately predicts all the electron energies. Previous models had not been able to explain the spectra. Using Bohr’s model of the atom the previously observed atomic line spectrum for hydrogen could be explained. No other model had done this before and was a big step towards the development of quantum mechanics. It is the first atom model that accounts for quantized or discrete energy steps. Thomson in 1904), the Saturnian model (by Hantaro Nagaoka in 1904), and the Rutherford model (by Ernest Rutherford in 1911).īohr’s model is different from the preceding model (the Rutherford model) because electrons can only orbit at certain radii or energy. The Bohr model replaced earlier models such as the plum-pudding model (by J.J. (From Wikipedia Commons) Improvements From Previous Models Each orbit change has a unique energy difference.Ītomic line spectra of hydrogen. And the blue line would be caused by an electron moving from shell 3 to shell 2. For example, the red line would be caused by the electron moving from shell 2 to shell 1. Only light of specific energy (or color) is released, shown by the sharp lines seen in the spectra, not all colors of light. These discrete energy steps are what cause atomic line spectra, like the one seen for hydrogen below. The energy is released in the form of light. When the electron moves from a larger higher-energy shell to a smaller lower-energy one it releases energy. When an electron moves to a smaller shell, it releases energy which we observe as light. The amount of energy absorbed or emitted is dependent on the difference in energy between the shells. For an electron to move to another shell it must absorb or release energy. The closer the shell is to the nucleus, the smaller the energy of that shell. Electrons (blue) orbit in circular shells around the nucleus (red).Įach shell has a specific energy level, and electrons cannot exist outside of these orbits. In this atomic model, all electrons must exist in a discrete shell and can’t be between shells. The planets are held in orbit by gravitational force and the electrons are held in their orbit by the electrostatic or Coulomb force between the electrons and protons. The electrons orbit around the nucleus similar to how planets orbit around the sun. The model is also referred to as the planetary model of an atom. In this model, the electrons travel around the nucleus of an atom in distinct circular orbits, or shells. The model was proposed by physicist Niels Bohr in 1913. In this tutorial, you will learn what the Bohr Model is, how it improved upon previous models of the atom, and what problems the Bohr model fails to solve.

Bohr model of potassium atom