They are exploding in all kinds of bright colors: red, green. ( Spectra used with permission from Prof. The Bohr Model and Atomic Spectra Imagine it is a holiday, and you are outside at night enjoying a beautiful display of fireworks. The colors of the discharge lamps are shown on the right. The line spectra of excited hydrogen, neon, and argon atoms the photon wavelength and frequency scales are shown on top. Passing the purple light through a prism produces the uppermost line spectrum shown in the figure: the purple color consists of four discrete visible wavelengths: 656.4 nm, 486.2 nm, 434.1 nm, and 410.2 nm. If we were to look through a telescope into outer space, we would be able to use a spectroscope and see the emission spectra that are present in order to determine the elements that are out there. For example, when electricity passes through a tube containing H 2 gas at low pressure, the H 2 molecules are broken apart into separate H atoms and the H atoms emit a purple color. We can use atomic emission light spectra to determine what elements are present in certain substances because we know that each element has a unique spectrum. Line spectra were intriguing because there was no reason to expect that some frequencies would be preferred over others.Įach element displays its own characteristic set of lines. Introduction to the Theory of Atomic Spectra is a systematic presentation of the theory of atomic spectra based on the modern system of the theory of. Light and Atomic Spectra In the 1670s, Isaac Newton, during optical experiments observed that a beam of white light was decomposed in a continuum spectrum. Interestingly, the photons emitted by the higher-energy atoms have only a few specific energies, thereby producing a line spectrum consisting of very sharp peaks (lines) at a few specific frequencies. For instance, the colors of “neon” signs are produced by passing electric current through low-pressure gases. These higher energy atoms can then release the additional energy by emitting photons. Niels Bohr explained the line spectrum of the hydrogen atom by assuming that the electron moved in circular orbits and that orbits with only certain radii were allowed. Heating a gaseous element at low pressure or passing an electric current through the gas imparts additional energy into the atoms. Atoms of individual elements emit light at only specific wavelengths, producing a line spectrum rather than the continuous spectrum of all wavelengths produced by a hot object.
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