When an electron transitions from an excited state (higher energy orbit) to a less excited state, or ground state, the difference in energy is emitted as a photon. If the atom receives energy from an outside source, it is possible for the electron to move to an orbit with a higher n value and the atom is now in an excited electronic state (or simply an excited state) with a higher energy. When the electron is in this lowest energy orbit, the atom is said to be in its ground electronic state (or simply ground state). Thus, the electron in a hydrogen atom usually moves in the n = 1 orbit, the orbit in which it has the lowest energy. One of the fundamental laws of physics is that matter is most stable with the lowest possible energy. The lowest few energy levels are shown in Figure 6.14. Since the Rydberg constant was one of the most precisely measured constants at that time, this level of agreement was astonishing and meant that Bohr’s model was taken seriously, despite the many assumptions that Bohr needed to derive it. When Bohr calculated his theoretical value for the Rydberg constant, R ∞, R ∞, and compared it with the experimentally accepted value, he got excellent agreement. Which is identical to the Rydberg equation in which R ∞ = k h c. The energy absorbed or emitted would reflect differences in the orbital energies according to this equation:ġ λ = k h c ( 1 n 1 2 − 1 n 2 2 ) 1 λ = k h c ( 1 n 1 2 − 1 n 2 2 ) Bohr assumed that the electron orbiting the nucleus would not normally emit any radiation (the stationary state hypothesis), but it would emit or absorb a photon if it moved to a different orbit. Instead, he incorporated into the classical mechanics description of the atom Planck’s ideas of quantization and Einstein’s finding that light consists of photons whose energy is proportional to their frequency. In 1913, Niels Bohr attempted to resolve the atomic paradox by ignoring classical electromagnetism’s prediction that the orbiting electron in hydrogen would continuously emit light. This loss in orbital energy should result in the electron’s orbit getting continually smaller until it spirals into the nucleus, implying that atoms are inherently unstable. This classical mechanics description of the atom is incomplete, however, since an electron moving in an elliptical orbit would be accelerating (by changing direction) and, according to classical electromagnetism, it should continuously emit electromagnetic radiation. The electrostatic force attracting the electron to the proton depends only on the distance between the two particles. The simplest atom is hydrogen, consisting of a single proton as the nucleus about which a single electron moves. This picture was called the planetary model, since it pictured the atom as a miniature “solar system” with the electrons orbiting the nucleus like planets orbiting the sun. Use the Rydberg equation to calculate energies of light emitted or absorbed by hydrogen atomsįollowing the work of Ernest Rutherford and his colleagues in the early twentieth century, the picture of atoms consisting of tiny dense nuclei surrounded by lighter and even tinier electrons continually moving about the nucleus was well established.Describe the Bohr model of the hydrogen atom.It predicted a number of experimental results and was gradually accepted among physicists.By the end of this section, you will be able to: Over the next decade the theory was further developed and modified by Niels Bohr and others. Niels Bohr published his ideas in three articles in 1913. "As soon as I saw Balmer’s formula, it was immediately clear to me,” said Niels Bohr later. It turned out that Niels Bohr’s theory accurately predicted this formula. Balmer’s formula in experimental spectroscopy, an empirically derived formula that described, but did not explain, the spectrum of the hydrogen atom. Hansen brought to his attention physicist J. At the beginning of 1913, his colleague H. Niels Bohr continued to work on his atomic model in the fall. The system worked so well that Margrethe became her husband’s secretary. He dictated and his bride wrote with clear, legible handwriting and she also improved his English. There Niels Bohr completed his first written work. Immediately after the wedding they travelled to Norway, where they would spend a few days. Niels Bohr returned to Copenhagen at the end of July 1912, and on the first of August he married Margrethe Nørlund. Yet during that short time he had formulated ideas that would soon lead to a revolution in physics. He had only been in Manchester for four months. Niels Bohr on the way home to Copenhagen.
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