OBJECTIVES
- To learn to use a spectroscope to study the lines in the emission spectra of atoms.
- To calibrate the spectroscope in order to convert scale readings into wavelengths; to understand
the calibration proce
...
OBJECTIVES
- To learn to use a spectroscope to study the lines in the emission spectra of atoms.
- To calibrate the spectroscope in order to convert scale readings into wavelengths; to understand
the calibration process.
- To examine the spectral lines of hydrogen in the visible region and correlate these lines to
hydrogen electronic transitions.
- To study the emission spectra of metals present in salts.
INTRODUCTION
Spectroscopy
The interaction of light with matter produces many interesting phenomena that are easily observed on
a daily basis. For example, the color of the sky is due to sunlight being scattered by molecules in the
air: the shorter-wavelength blue light is scattered more than longer-wavelength red light thus causing
the sky to appear blue. Similarly, a rainbow after a storm is the result of light passing through prismlike raindrops, which break the light into its component colors. A dilute solution of powdered milk
(which contains protein macromolecules that can scatter light) appears opalescent blue.
In this experiment, you will study the interaction between light and atoms. For most atoms at room
temperature, the electrons occupy the lowest allowed energy level, known as the ground state. When
atoms are energized by an electric discharge, by a flame, or by light, electrons are excited from the
lower level to higher energy levels known as excited states. These excited atoms can emit photons of a
particular wavelength and drop down to lower energy levels. If the emitted light is passed through a
narrow slit and then through a prism or diffraction grating, an emission spectrum is observed.
According to quantum theory, the energy content of an atom is quantized; that is, the energy can have
only certain discrete values. The allowed energy levels are characteristic of each particular kind of
atom. Through the technique of emission spectroscopy, the allowed energy levels can be probed.
Quantum theory describes light as being composed of tiny bundles of energy called photons. Different
colors of light are produced by photons of different wavelengths. The energy of a photon E is related
to its wavelength λ by the equation:
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