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Learning Objectives

At the end of this lab, students should know...

What is the fundamental principle in Bohr's model of the hydrogen atom?

Electrons orbit the nucleus in discrete energy states or orbitals and can only transition between them by absorbing or releasing energy. Electrons cannot exist between orbitals.

How are energy states described?

Energy states are described using quantum numbers. The quantum number n is used to label each energy state, where the lowest energy state is the ground state at n=1.

What is the difference between the emission spectra of pure elemental samples and samples containing a mixture of molecules?

The emission spectrum of a pure elemental sample will appear as spectral lines of discrete wavelengths, whereas a mixed sample will have an emission spectrum that is continuous over a range of wavelengths.

What electron transitions are described by the Balmer series?

The Balmer series includes the transitions from higher energy states (n=3-7) down to the n=2 energy state.

In what region of the electromagnetic spectrum are the Balmer series spectral lines?

The Balmer series spectral lines are in the visible region, with lines at 410.2 nm, 434.1 nm, 486.1 nm, and 656.3 nm.

List of Materials

  • Data acquisition device
    5
  • UV-Vis spectrophotometer
    5
  • Flash drive
    5
  • Power base for gas-discharge lamps
    1
  • Hydrogen lamp
    1
  • Helium lamp
    1
  • Neon lamp
    1

Lab Prep

Source: Smaa Koraym at Johns Hopkins University, MD, USA

  1. Preparation of the Laboratory

    Here, we show the laboratory preparation for 10 students working in pairs, with some excess. Please adjust quantities as needed.

    • To set up for this lab experiment, wear the appropriate personal protective equipment, including a lab coat, chemical splash goggles, and gloves.
    • Place a power base for gas discharge lamps in a central area.
    • Pick up the hydrogen lamp and clean it with a laboratory wipe before setting it in the designated slot of the power base. Then, plug in the lamp base.
    • Wipe the helium and neon lamps and return them to their storage compartment so that you can exchange the lamps when needed during the lab.
    • Assemble handheld UV-Vis spectrophotometers and distribute them to the lab stations to finish the setup.
    • During the lab, you will call up each student group to acquire a spectrum while you operate the hydrogen lamp for up to 30 s. Once all students have recorded a spectrum, you will repeat the process with the helium and neon lamps.
    • If a lamp is still hot when you are done with it, wait 5 min before removing it from the base.

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