[5] Line Spectra and the Bohr Model.pdf - 3/12/2021 6.3:...

This preview shows page 1 - 2 out of 9 pages.

The preview shows page 1 - 2 out of 9 pages.
3/12/20216.3: Line Spectra and the Bohr Model - Chemistry LibreTexts(Brown_et_al.)/06._Electronic_Structure_of…1/96.3: Line Spectra and the Bohr ModelTo know the relationship between atomic spectra and the electronic structure of atoms.The concept of the photon emerged from experimentation withthermal radiation, electromagnetic radiation emitted as theresult of a source’s temperature, which produces a continuous spectrum of energies.The photoelectric effect providedindisputable evidence for the existence of the photon and thus the particle-like behavior of electromagnetic radiation.However, more direct evidence was needed to verify the quantized nature of energy in all matter. In this section, we describehow observation of the interaction of atoms with visible light provided this evidence.Line SpectraAlthough objects at high temperature emit a continuous spectrum of electromagnetic radiation, a different kind of spectrum isobserved when pure samples of individual elements are heated. For example, when a high-voltage electrical discharge ispassed through a sample of hydrogen gas at low pressure, the resulting individual isolated hydrogen atoms caused by thedissociation of H emit a red light. Unlike blackbody radiation, the color of the light emitted by the hydrogen atoms does notdepend greatly on the temperature of the gas in the tube. When the emitted light is passed through a prism, only a few narrowlines of particular wavelengths, called aline spectrum, are observed rather than a continuous range of wavelengths (Figure). The light emitted by hydrogen atoms is red because, of its four characteristic lines, the most intense line in its spectrumis in the red portion of the visible spectrum, at 656 nm. With sodium, however, we observe a yellow color because the mostintense lines in its spectrum are in the yellow portion of the spectrum, at about 589 nm.Figure: The Emission of Light by Hydrogen Atoms. (a) A sample of excited hydrogen atoms emits a characteristic redlight. (CC BY-SA 3.0 Unported;Science Made AliveviaWikipedia) (b) When the light emitted by a sample of excited hydrogenatoms is split into its component wavelengths by a prism, four characteristic violet, blue, green, and red emission lines can beobserved, the most intense of which is at 656 nm. (CC BY-SA 3.0;Jan HomannviaWikipedia)Suchemission spectrawere observed for many other elements in the late 19th century, which presented a major challengebecause classical physics was unable to explain them. Part of the explanation is provided by Planck’s equation: the observationof only a few values of λ (or) in the line spectrum meant that only a few values ofEwere possible. Thusthe energy levels of ahydrogen atom had to be quantized; in other words, only states that had certain values of energy were possible, orallowed. If ahydrogen atom could haveanyvalue of energy, then a continuous spectrum would have been observed, similar to blackbody

Upload your study docs or become a

Course Hero member to access this document

Upload your study docs or become a

Course Hero member to access this document

End of preview. Want to read all 9 pages?

Upload your study docs or become a

Course Hero member to access this document

Term
Spring
Professor
N/A
Tags
Atom, Photon, line spectra

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture