Basic concepts of quantum mechanics: Difference between revisions

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A second, related, puzzle was the [[emission spectrum]] of atoms. When a gas is heated, it gives off light at certain discrete frequencies; for example, the visible light given off by [[hydrogen]] consists of four different colours, as shown in the picture below. In contrast, white light contains light at the whole range of visible frequencies.

[[File:Emission spectrum-H.pngsvg|757px|thumb|none|[[Emission spectrum]] of [[hydrogen]]. When excited, hydrogen gas gives off light in four distinct colours (spectral lines) in the visible spectrum, as well as a number of lines in the infra-red and ultra-violet.]]

In 1913 [[Niels Bohr]] proposed a new model of the atom that included quantised electron orbits. This solution became known as the Bohr model of the atom. In Bohr's model, electrons could inhabit only particular orbits around the atomic nucleus. When an atom emits or absorbs energy, the electron does not move in a continuous trajectory from one orbit around the nucleus to another, as might be expected in classical theory. Instead, the electron jumps instantaneously from one orbit to another, giving off the difference in energy as light in the form of a photon.<ref name="WorldBook"/>{{rp|6}} The possible energies of the photons given off by each element in the [[periodic table]] are determined by the difference in energy between the orbits, so the emission spectrum for each element will contain a number of lines.<ref>Dicke and Wittke, ''Introduction to Quantum Mechanics'', p. 10f.</ref> The Bohr model was able to explain the emission spectrum of hydrogen, but wasn't able to make accurate predictions for multi-electron atoms, or to explain why some spectral lines are brighter than others.