Investigation 26D: Identifying elements using spectroscopy

Essential questionsHow can you use spectroscopy to identify elements?
Every atomic element has a different number of protons and electrons, which means that every element has a unique set of energy levels. When an electron makes a transition between energy levels, a photon of light is either emitted or absorbed. Every element’s unique set of energy levels has a corresponding unique set of emission and absorption lines—a signature. In this investigation you will identify unknown elements using their spectroscopic signature.
Part 1: Hand-held visual spectrograph and discharge lamps

Calibrating the spectrograph and observing objectsSafety warning: Never point a spectrograph directly at the Sun or any other bright light source. Never touch discharge tubes because they can be very hot.
  1. Calibrate the hand-held visual spectrograph by pointing it at a fluorescent lamp and adjusting the scale to align the green line with 546 nm.
  2. Turn on the power for the discharge lamps.
  3. Point the spectrograph at the fluorescent lamp and discharge lamps.
  1. What elements can you identify in the overhead fluorescent lamp? Why?
  2. Based on the spectra you observe, which of the discharge lamps (H, He, Ne, or Ar) is which? Read the text aloud Show Some lines you might see
Part 2: Identifying mystery elements in spectra

Identifying mystery elements in spectra
  1. The first four sheets of emission-line spectra should be printed on clear transparencies. The other pages should be printed on white paper.
  2. Slide the transparencies over the mystery spectra to identify the element(s) they contain.
  1. How did you use the known atomic spectra to identify the unknown ones?
  2. Describe at least three physical properties that can be used to identify elements.
Read the text aloud
Part 3: Identifying elements in stars and the Sun

Identifying elements in the spectra of stars and the Sun
  1. Use the atomic spectra to identify elements in the absorption lines of various stars.
  1. How does an absorption-line spectrum differ from an emission-line spectrum?
  2. Which star(s) show evidence for heavier elements? Why might this happen?
Read the text aloud

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