FIS 340 Survival Guide Part 2 Exam Review
Questions with Verified Correct Answers
Spectroscopy
The interaction of light and matter.
Ways molecules interact with light
diffraction, refraction, radiation, absorption, emission, etc.
What are the properties that explain the behavior of light?
Wavelength and Particles
Light Wave Characteristics
Amplitude
Wavelength
UV-Spectroscopy Characteristics
Wavelength
Frequency
Beer's Law
A=ebc
What is A in Beer' Law?
Absorbance
What is e in Beer's law?
The Molar Absorbance Constant
What is b in Beer's Law?
Path Length
What is the C in Beer's Law?
Concentration of Sample
,What are the three types of electronic transitions?
Transitions involving p,s, and n electrons
Charge transfer of electrons
Transitions involving d and f electrons
What is the p,s,n transition that requires the least energy
n-Pi
How exactly does UV-Vis separate
Different molecules absorb radiation of different wavelengths
Why are UV-Vis bands wide?
When an atom absorbs energy, electrons are promoted from their ground to an excited state;
Vibrations/Rotations have their own energy that overlaps causing something that looks like a
continuous band
Absorption Shift types
Hypochromic (Blue Shift)
Bathochromic (Red Shift)
Absorption Shift
Molecule's medium (solvent) also interacts with the absorption process
hypsochromic shift
(Blue Shift) Peaks resulting from n-Pi transitions are shifted to shorter wavelength with
increasing solvent polarity
bathochromic shift
(Red Shift) Seen for Pi-Pi transitions with increasing solvent polarity
How do you determine a solvent for UV-Vis?
Use the cutoff of wavelengths to determine if a solvent is good to use
What is the Ultra-violet range?
1900-400nm
What is the Visible Light Range?
400-800nm
, What is the Infrared Range?
800-100,000nm
What is the difference between polar and non-polar solvents when used in UV-Vis?
Generally:
Polar Solvents tend to make broader bands due to vibrational interactions, while nonpolar
solvents produce sharper bands
Molar Spectroscopy
Combination of atoms into molecules creates unique energetic states and therefore unique
spectra of the transitions between states
What are some ways that molecular spectra can be obtained?
Electron spin-states
molecular rotations
molecular vibrations
electronic states
What does a spectrophotometer measure?
Amount of light transmitted through a solution
Absorbance
Percent of transmitted light; directly proportional to concentration
General Setup of UV-Vis
Lamp>Monochromator>Sample Area>Detector
Lamp (UV-Vis)
Ideal source yields a constant intensity across all wavelengths with low noise and long-term
stability; Emits light across a range of wavelengths
Commonly used lamps in UV-Vis
Deuterium Arch Lamp (Ultraviolet)
Tungsten Halogen Lamp (Part Ultra-violet/Visible Range)
Xenon Lamp (Entire Ultraviolet and Visible Range)
Monochromator (UV-Vis)
Questions with Verified Correct Answers
Spectroscopy
The interaction of light and matter.
Ways molecules interact with light
diffraction, refraction, radiation, absorption, emission, etc.
What are the properties that explain the behavior of light?
Wavelength and Particles
Light Wave Characteristics
Amplitude
Wavelength
UV-Spectroscopy Characteristics
Wavelength
Frequency
Beer's Law
A=ebc
What is A in Beer' Law?
Absorbance
What is e in Beer's law?
The Molar Absorbance Constant
What is b in Beer's Law?
Path Length
What is the C in Beer's Law?
Concentration of Sample
,What are the three types of electronic transitions?
Transitions involving p,s, and n electrons
Charge transfer of electrons
Transitions involving d and f electrons
What is the p,s,n transition that requires the least energy
n-Pi
How exactly does UV-Vis separate
Different molecules absorb radiation of different wavelengths
Why are UV-Vis bands wide?
When an atom absorbs energy, electrons are promoted from their ground to an excited state;
Vibrations/Rotations have their own energy that overlaps causing something that looks like a
continuous band
Absorption Shift types
Hypochromic (Blue Shift)
Bathochromic (Red Shift)
Absorption Shift
Molecule's medium (solvent) also interacts with the absorption process
hypsochromic shift
(Blue Shift) Peaks resulting from n-Pi transitions are shifted to shorter wavelength with
increasing solvent polarity
bathochromic shift
(Red Shift) Seen for Pi-Pi transitions with increasing solvent polarity
How do you determine a solvent for UV-Vis?
Use the cutoff of wavelengths to determine if a solvent is good to use
What is the Ultra-violet range?
1900-400nm
What is the Visible Light Range?
400-800nm
, What is the Infrared Range?
800-100,000nm
What is the difference between polar and non-polar solvents when used in UV-Vis?
Generally:
Polar Solvents tend to make broader bands due to vibrational interactions, while nonpolar
solvents produce sharper bands
Molar Spectroscopy
Combination of atoms into molecules creates unique energetic states and therefore unique
spectra of the transitions between states
What are some ways that molecular spectra can be obtained?
Electron spin-states
molecular rotations
molecular vibrations
electronic states
What does a spectrophotometer measure?
Amount of light transmitted through a solution
Absorbance
Percent of transmitted light; directly proportional to concentration
General Setup of UV-Vis
Lamp>Monochromator>Sample Area>Detector
Lamp (UV-Vis)
Ideal source yields a constant intensity across all wavelengths with low noise and long-term
stability; Emits light across a range of wavelengths
Commonly used lamps in UV-Vis
Deuterium Arch Lamp (Ultraviolet)
Tungsten Halogen Lamp (Part Ultra-violet/Visible Range)
Xenon Lamp (Entire Ultraviolet and Visible Range)
Monochromator (UV-Vis)
