Chemlab: Chemistry 6


Spectrum of the Hydrogen Atom

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Applets

Atomic Spectra Applet
The first part of this applet shows a schematic diagram of a meterstick spectroscope. You can move the eye of an observer until a spectral line is viewed and clearly see the geometry of the experiment. You can also look at the spectra of the different elements available in the lab this week, to see how they compare.

The second part of this applet shows the energy levels for an electron in a hydrogen atom. You can examine transitions between different energy levels and see where the emitted light would appear in the observed spectrum of the element.

Goals
In the first part of this experiment you will use a meterstick spectroscope to determine the wavelengths of visible light emitted by a hydrogen atom. The wavelengths of the emitted photons will be converted to photon energies which will then be used to identify the change in atomic energy level which gave rise to the emitted photon. The Bohr model will be used to provide the required expressions for the allowed discrete energy levels for a one-electron atom. In the second part of the experiment, you will observe the spectrum of the sodium atom in the same way. From the measured spectrum and the ground state sodium atom ionization energy you will be able to calculate the effective nuclear charge for a 3s and a 3p electron in the sodium atom. Finally, you will compare qualitatively the spectra of a series of elements and the light emitted by a fluorescent lamp.

Key Questions
Why are atomic spectra composed of light emitted in discrete lines, rather than continuous bands?

How are the energy of the light emitted and the energy of the electron in the atom related?

How are single- and multi-electron atoms different? What do the electron energies depend on, in each case?

What is effective nuclear charge? Why is it different for a sodium electron in a 3p orbital and a 3s orbital?

Why do different elements have different spectra?

How do fluorescent lights work? What element do they contain?
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