The emission line spectra of hydrogen, lithium, sulfur, and selenium for the visible region of the spectrum are shown below. If a sample contains more than one of these elements, which of the following spectra would correspond to a sample containing both S and Se?

Question

The emission line spectra of hydrogen, lithium, sulfur, and selenium for the visible region of the spectrum are shown below.  If a sample contains more than one of these elements, which of the following spectra would correspond to a sample containing both S and Se?

Quizplus · Accepted Answer

11ecba2d_1236_5d3f_a3bf_89e112ce4b86_MD0008_00 Electrons within an atom can exist only in particular, discrete energy levels that are identified by quantum numbers (such as the principle quantum number n) and by orbital designations. An electron excited from a lower to a higher energy level must absorb an amount of energy equal to the energy difference between the two levels, but an electron moving from a higher to a lower energy level releases energy (in the form of a photon) with an energy equal to the energy difference between the levels. Because each element has a unique electron configuration, excited electrons in a gas-phase sample of a pure element emit photons only at specific wavelengths rather than as a continuous spectrum. This produces a line spectrum with emission lines at particular wavelengths that are characteristic of the given element and its electron configuration. As a result, the line spectrum of each element is unique and can be used like a fingerprint to identify elements. As seen from the reference spectra given for this question, each element has a different spectral pattern. Moreover, S and Se also have distinctive lines in the range of 575-650 nm, which are absent in the spectra of Li and H. Specifically, Se displays a line near 585 nm, whereas S displays a line near 630 nm. As such, the line spectrum of a sample mixture that contains both S and Se must have the spectral patterns of S and Se, which includes lines at both 585 and 630 nm. Of the four choices, only (Choice D) is a match. (Choice A) This is the line spectrum of a mixture of H and Li, which lacks the lines indicative of S and Se. (Choice B) This is the line spectrum of a mixture of H and S, which lacks the lines indicative of Se. (Choice C) This is the line spectrum of a mixture of H and Se, which lacks the lines indicative of S. Educational objective: Each element emits photons only at specific wavelengths to give a unique emission line spectrum corresponding to its electron configuration.

The Emission Line Spectra of Hydrogen, Lithium, Sulfur, and Selenium