What personal protective equipment is required before starting a Balmer Series lab?

Before beginning the lab, wear a lab coat, chemical splash goggles, and gloves to ensure proper safety. These items protect you from potential chemical exposure and hazards during the experiment. Always put on all required PPE before handling any equipment or materials in the laboratory.

How should you prepare the hydrogen lamp before the experiment begins?

Clean the hydrogen lamp with a laboratory wipe before placing it in the designated slot of the power base. Once positioned correctly, plug in the lamp base to activate it. This preparation ensures the lamp is clean and ready to produce accurate spectra for student observations.

What is the proper procedure for exchanging gas discharge lamps during the lab?

Wipe the helium and neon lamps and store them in their designated compartment when not in use. When ready to exchange lamps, retrieve the next lamp from storage and place it in the power base slot. This organized approach allows efficient lamp switching while maintaining equipment cleanliness throughout the experiment.

How long should students have access to the hydrogen lamp for spectrum acquisition?

Each student group has up to 30 seconds to acquire a spectrum while you operate the hydrogen lamp. Once all students have recorded their data, you repeat the process with helium and neon lamps. This time allocation ensures fair access and efficient use of equipment across all lab pairs.

What equipment is distributed to individual lab stations for this experiment?

Handheld UV-Vis spectrophotometers are assembled and distributed to each lab station to enable spectrum acquisition. These instruments allow students to measure and record the spectral data from each gas discharge lamp. Proper distribution ensures all student groups can simultaneously collect their observations.

Why must you wait before removing a hot lamp from the power base?

If a lamp is still hot after use, wait 5 minutes before removing it from the base to prevent burns and equipment damage. This cooling period allows the lamp to reach a safe temperature for handling. Following this safety protocol protects both you and the equipment from thermal injury.

Balmer Series

Concepts Instructor Prep Student Protocol

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Atoms and molecules exhibit very interesting behavior when they absorb and release energy. The electrons in an atom traditionally exist at their lowest energy state, called the ground state, and labeled as n equal to one. However, when an atom absorbs energy, the electrons become excited and move to a higher energy level. When the electrons relax down to either a lower energy state or to the ground state, the excess energy is released as emitted light.

You may be familiar with these energy states, as they are depicted in the Bohr Model, which describes an atom as a nucleus with orbiting electrons in shells or orbitals. These shells are the same as the energy levels and are labeled by n. The wavelength of the emitted light depends on the difference between the high and low energy levels. High energy emitted light results from electrons relaxing from a higher energy level, and low energy emitted light results from electrons relaxing from a lower energy level.

The emission spectrum is a measure of emitted radiation across a range of wavelengths. With pure elemental species, the emission behavior appears as lines of specific wavelengths rather than a broad spectrum. Since different atoms have different energy levels, these spectral lines vary from element to element and depend on the transitions those electrons make between energy states when excited. For example, there are six named series of spectral lines for hydrogen, one of which is the Balmer Series.

The Balmer Series of spectral lines occurs when electrons transition from an energy level higher than n = 3 back down to n = 2. The visible light spectrum for the Balmer Series appears as spectral lines at 410, 434, 486, and 656 nm. The h alpha line is the red line at 656 nm and occurs due to the transition from n= 3 to n = 2. The cyan, blue, and violet lines correspond to energy level transitions from n = 4, 5, and 6, respectively, back down to n = 2. Additional spectral lines can be measured outside of the visible range.

Johann Balmer quantified the visible lines using the Balmer formula. Here, lambda is the observed wavelength, c is a constant, n is the lower energy level of two, and m is the higher energy level. The combination of the Balmer equation and the Bohr Model gives us the Rydberg equation, which describes the spectral lines of many different elements. In this equation, lambda is the recorded wavelength, and R_H is the Rydberg constant. The initial levels marked by n-initial represent the higher energy level that the electrons excite to and n final is the lower energy level that the electrons relax back to. For the Balmer series, n_final = 2.

In this lab, you will measure and observe the emission spectrums of hydrogen, helium, and neon and use the Rydberg Equation to determine the location of the spectral lines.

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

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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.