Luckily, science was ready for the challenge Physicists such as Niels Bohr continued to design experiments to test the nuclear model of the atom, which eventually evolved into the modern quantum mechanical model. Bohrs model suggests that each atom has a set of unchangeable energy levels, and electrons in the electron cloud of that atom must be in one of those energy levels. Concept check: Thomson proposed an atomic model with distinct negative charges floating within a 'sea' of positive charge. The negative sign in Equation 5.4.5 and Equation 5.4.6 indicates that energy is released as the electron moves from orbit n2 to orbit n1 because orbit n2 is at a higher energy than orbit n1. 2.12: The Bohr Model - Atoms with Orbits is shared under a CK-12 license and was authored, remixed, and/or curated by Marisa Alviar-Agnew & Henry Agnew. Bohr’s model required only one assumption: The electron moves around the nucleus in circular orbits that can have only certain allowed radii. 1 ( 1 n2 2 1 n2 1) Except for the negative sign, this is the same equation that Rydberg obtained experimentally. (It was a running joke that any theory of atomic and molecular spectra could be destroyed by throwing a book of data at it, so complex were the spectra. In 1913, a Danish physicist, Niels Bohr (18851962 Nobel Prize in Physics, 1922), proposed a theoretical model for the hydrogen atom that explained its emission spectrum. But, in spite of years of efforts by many great minds, no one had a workable theory. Learn about the Bohr model of the atom, a modification of Rutherfords model that explains electrons in fixed orbits around a nucleus. Figure 30.14 Niels Bohr, Danish physicist, used the planetary model of the atom to explain the atomic spectrum and size of the hydrogen atom. It does introduce several important features of all models used to describe the distribution of electrons in an atom. The Bohr model shows that there are 2 electrons in the innermost shell, then 8, 18 and so on, but it doesnt have an explanation for why that is the case. Bohr’s model of the hydrogen atom provides insight into the behavior of matter at the microscopic level, but it does not account for electronelectron interactions in atoms with more than one electron.

The main reason is because it offers explanatory as well as descriptive and predictive power.

Maxwell and others had realized that there must be a connection between the spectrum of an atom and its structure, something like the resonant frequencies of musical instruments. This is why the quantum theory is more powerful than Bohrs theory: its explanatory power.

Bohr's model of the atom