Helium Bohr model

Despite its great success in accounting for the spectral lines of the H atom, the Bohr model failed to predict the spectrum of any other atom, even that of helium, the next simplest element. In essence, the Bohr model predicts spectral lines for the H atom and other one-electron species, such as He" (Z = 2), Li (Z = 3), and Be (Z = 4). But, it fails for atoms with more than one electron because in these systems, electron-electron repulsions and additional nucleus-electron attractions are present as well. Nevertheless, we still use the terms ground state and excited state and retain one of Bohr s central ideas in our current model the energy of an atom occurs in discrete levels. 

The Bohr model gave the correct energies for the hydrogen atom but failed when applied to helium. Hence, in the early days of quantum mechanics, it was important to show that the new theory could give an accurate treatment of helium. The pioneering work on the helium ground state was done by Hylleraas in the years 192 1930. To allow for the effect of one electron on the motion of the other, Hylleraas used variational functions that contained the interelectronic distance ri2- One function he used is... 

In spite of its success with the hydrogen atom, the Bohr model was deficient because it was unable to account for the emission spectra of heavier atoms, such as helium. 

Sir Ernest Rutherford (1871-1937 Nobel Prize for chemistry 1908, which as a physicist he puzzled over) was a brilliant experimentalist endowed with an equal genius of being able to interpret the results. He recognized three types of radiation (alpha, beta, and gamma). He used scattering experiments with alpha radiation, which consists of helium nuclei, to prove that the atom is almost empty. The diameter of the atomic nucleus is about 10 000 times smaller than the atom itself. Furthermore, he proved that atoms are not indivisible and that in addition to protons, there must also be neutrons present in their nucleus. With Niels Bohr he developed the core-shell model of the atom. 

The reaction to Bohr s model is understandable. Bohr s atomic model was based on older laws of physics with quantum assertions added. As such, it was clearly a jumbled affair. But the model provided a pictorial explanation of the origin of spectral lines and from the model the wavelengths of the Balmer series could be calculated. The model failed for the next simplest atom, helium. Had... 

There were however serious problems with Bohr s neat picture, the most catastrophic of which was that the model was exact only for hydrogen. Helium, with two electrons, was already too complicated for the model to handle exactly. But a new approach would soon be born and born out of war. During World War I, Louis de Broglie, a young French aristocrat who had been interested in history, was assigned to a radio communications unit, and he became interested in radio waves. 

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