![]() Under these circumstances, no electron could lose energy because no electron could move down to a lower energy level. The electrons orbit around the nucleus similar to how planets orbit. 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. Bohr worked out rules for the maximum number of electrons that could be in each energy level in his model, and required that an atom in its normal state (ground state) had all electrons in the lowest energy levels available. The Bohr Model is a structural model of an atom. In this situation, no person could move down because all of the lower rungs are full. If the ladder had five people on it, they would be on the lowest five rungs. Other rules for the ladder are that only one person can be on a rung in the normal state, and the ladder occupants must be on the lowest rung available. Bohr's model calculated the following energies for an electron in the shell, n : E ( n) 1 n 2 13. Suppose we had such a ladder with 10 rungs. Bohr's model of hydrogen is based on the nonclassical assumption that electrons travel in specific shells, or orbits, around the nucleus. The only way you can be on that ladder is to be on one of the rungs, and the only way you could move up or down would be to move to one of the other rungs. It would be like a ladder that had rungs only at certain heights. The energy levels are quantized, meaning that only specific amounts are possible. Note that the spacing between rungs gets smaller at higher energies (CC BY-NC Ümit Kaya)īohr hypothesized that the only way electrons could gain or lose energy would be to move from one energy level to another, thus gaining or losing precise amounts of energy. That is a reason not to teach about circular orbits and L = nħ.\): The energy levels of the electrons can be viewed as rungs on a ladder. The existence of the atomic spectra is support for Bohr's model of the atom. But second, it doesn’t conform to the essence of what Bohr actually did. Bohr's model suggests that the atomic spectra of atoms is produced by electrons gaining energy from some source, jumping up to a higher energy level, then immediately dropping back to a lower energy level and emitting the energy difference between the two energy levels. This, in itself, is not a reason to scrap it, for the historical development of quantum physics is certainly of interest. First it doesn’t conform to our present understanding of the hydrogen atom. This picture of the hydrogen atom is wrong in two senses. This “pedagogic” version postulates that an electron in a stationary state moves in a circular orbit with an angular momentum that is an integral multiple of h/2π ( L = nh/2π = nħ)- ħ for the lowest-energy state, 2 ħ for the next state, and so on. Unfortunately, the version of the Bohr atom that appears in many textbooks and is no doubt often presented to students is more wrong than right and may leave both teachers and students wondering why, more than a hundred years later, it is still being taught. ![]() This is an excellent idea, given the historic importance of Bohr’s 1913 work, which provided the bridge from Planck’s quantized interaction of matter and radiation (1900) to the full theory of quantum mechanics (1925-28). Many teachers like to introduce the Bohr atom toward the end of an introductory physics course.
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