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Questions and Answers
What is the most important step in atomic spectroscopic procedures?
What happens to the molecule during atomization?
What is the purpose of the radiation source in AAS?
What is the result of the atoms absorbing radiation in AAS?
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What is the relationship between the intensity of the absorbed light and the concentration of the atoms?
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What is the equation that describes the relationship between the intensity of the radiation and the concentration of the atoms?
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What is the purpose of the chopper in an atomic absorption spectrometer?
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What is the function of the monochromator in an atomic absorption spectrometer?
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What is the function of the detector in an atomic absorption spectrometer?
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What is the read-out device in an atomic absorption spectrometer used for?
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Study Notes
Atomic Absorption Spectroscopy (AAS) and Atomic Emission Spectroscopy (AES)
- AAS is a method that uses the absorption of light to determine elements (atoms) in a sample, requiring atomization of the sample.
- AES is a method that uses the emission of light to determine elements in a sample, also requiring atomization.
Energy Level Diagram
- Different atoms have different energy transition levels.
- Energy level diagram shows valence electron transitions.
- Atomic absorption and emission of light are associated with transitions of electrons between different energy levels.
Absorption and Emission Spectra
- Absorption spectra: atom absorbs light of a particular wavelength, consuming energy.
- Emission spectra: atom emits light of a particular wavelength, releasing energy.
- Atomic spectra: line spectra provide specificity, as each element has its own pattern due to its unique electronic configuration.
Atomic vs. Molecular Spectra
- Atoms: only electronic transition states, resulting in line spectra.
- Molecules: undergo rotational, vibrational, and electronic transitions, resulting in band spectra.
Instrument Components
- UV-Vis Spectrometer: light source, monochromator, sample, detector, and read-out system.
- AAS Spectrometer: light source, monochromator, atomizer, detector, and read-out system.
- AES Spectrometer: light source, monochromator, atomizer, detector, and read-out system.
Flame Spectroscopy
- Flame Spectroscopy is the study of absorption/emission of electromagnetic radiation by monatomic particles in the gaseous state present in the flame.
- Flame is used as a source of radiation in qualitative methods like flame tests.
Flame Test
- Observation of different colored flames can be used to identify elements:
- Sodium: golden-yellow
- Potassium, cesium: violet (lilac)
- Lithium: carmine-red
- Calcium: brick-red
- Strontium: crimson
- Barium, molybdenum: yellowish-green
- Borates, copper, thallium: green
- Lead, arsenic, antimony, bismuth, copper: blue
Theory of Atomic Absorption
- Atomization: a process that produces atoms in the gaseous state.
- Atoms in the vapor state absorb radiation of a specific wavelength, promoting outermost electrons to higher energy levels.
- The intensity of absorbed light is proportional to the concentration of atoms in the flame.
Beer-Lambert's Law
- Log (I0/I) = a x b x c, where:
- a is the absorption coefficient of the element at the appropriate wavelength
- b is the path length through the flame (standard and constant for each instrument)
- c is the total concentration of the atom in the test solution
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Description
This quiz covers the principles of Atomic Absorption Spectroscopy (AAS) and energy level transitions in atoms.
