Analytical Chem istry - DePauw University

546 Analytical Chemistry 2.0Example 10.1In 1817, Josef Fraunhofer studied the spectrum of solar radiation, observinga continuous spectrum with numerous dark lines. Fraunhofer labeledthe most prominent of the dark lines with letters. In 1859, Gustav Kirchhoffshowed that the D line in the sun’s spectrum was due to the absorptionof solar radiation by sodium atoms. The wavelength of the sodium D lineis 589 nm. What are the frequency and the wavenumber for this line?So l u t i o nThe frequency and wavenumber of the sodium D line are8c 300 . × 10 m/sν = == 509 . × 10−9λ 589×10 ms14 −11 1ν = =λ 589×10−91 m× = 170 . × 10m 100 cmcm4 −1Practice Exercise 10.1Another historically important series of spectral lines is the Balmer seriesof emission lines form hydrogen. One of the lines has a wavelength of656.3 nm. What are the frequency and the wavenumber for this line?Click here to review your answer to this exercise.Pa r t i c l e Pr o p e r t i e s o f El e c t r o m a g n e t i c RadiationWhen matter absorbs electromagnetic radiation it undergoes a change inenergy. The interaction between matter and electromagnetic radiation iseasiest to understand if we assume that radiation consists of a beam of energeticparticles called photons. When a photon is absorbed by a sampleit is “destroyed,” and its energy acquired by the sample. 3 The energy of aphoton, in joules, is related to its frequency, wavelength, and wavenumberby the following equalitieshcE = hν= = hcνλwhere h is Planck’s constant, which has a value of 6.626 10 –34 J . s.Example 10.2What is the energy of a photon from the sodium D line at 589 nm?So l u t i o nThe photon’s energy is3 Ball, D. W. Spectroscopy 1994, 9(6) 20–21.