Spectroscopy
Electronic
Structure
of Atoms
© 2009, Prentice-Hall, Inc.
Types of Spectroscopy
• Mass spectrometry
Spectroscopy based on the interaction of EMR with
matter:
• Infrared radiation is associated with transitions in molecular
vibrations
• UV/Visible radiation is associated with transitions in electronic
energy levels
- Spectrophotometry
- Photoelectronic spectroscopy (PES)
Electronic
Structure
of Atoms
© 2009, Prentice-Hall, Inc.
Mass Spectrometry
• See Mass Spectrometry POGIL for details
• used to identify the elements and the masses
of individual atoms of a specific element
(isotopes)
 estimate average atomic mass
• used to identify molar mass of molecules,
especially large organic molecules such as
proteins
Electronic
Structure
of Atoms
© 2009, Prentice-Hall, Inc.
Infrared (IR) Spectroscopy
• can be used to detect the presence of
different types of bonds (IR is
associated with transitions in molecular
vibrations)
• e.g. organic chemistry: functional
groups, double and triple bonds
Electronic
Structure
of Atoms
© 2009, Prentice-Hall, Inc.
Spectrophotometry
• Exploits the absorption of EMR (e.g. visible
light) by solutions
• Beer-Lambert Law: A = abc, i.e. direct
relationship between absorbance and
concentration
• Standard curve (which is linear) of A vs.
concentration  concentration of unknown
• See notes, quiz, reading assignment from S1
Electronic
for details
Structure
of Atoms
© 2009, Prentice-Hall, Inc.
Photoelectron Spectroscopy
(PES)
• Quantifiable application of the
photoelectric effect
• If light shining on a material (especially a
metal) has sufficient energy it is able to
eject electrons from that material (Each
photon: E=hn, see Ch. 6)
• Photoelectron spectroscopy determines
the amount of energy needed to do so.
Electronic
Structure
of Atoms
© 2009, Prentice-Hall, Inc.
Photoelectron Spectroscopy
(PES)
• Measurement of these energies 
deduce the structure of the atom
• Intensity of the signal  number of
electrons at that energy level
• Note: energy is measured in eV or
MJ/mole electrons
Electronic
Structure
of Atoms
© 2009, Prentice-Hall, Inc.
Example of PES
Generated by the simulation at; http://www.chem.arizona.edu/chemt/Flash/photoelectron.html
What does this mean?
Another way to view ionization energy
From Adrian Dingle’s blog, Jan. 29, 2013
http://www.adriandingleschemistrypages.com/ap/summary-of-additions-to-new-ap-chemistry-curriculum-part-1-pes/
Electronic
Structure
of Atoms
© 2009, Prentice-Hall, Inc.
PES Example Questions
If the question flagged Mg as the
element in question:
a. Which peak in the spectrum
represents electrons that are
closest to the nucleus?
a. What is the relevance of the
relative height of the peaks at
5.31 and 9.07 eV?
a. Why is there such a large
difference in energy between
the peaks at 0.74, 5.31 and
9.07 eV and the peak at 126
eV?
From Adrian Dingle’s blog:
http://www.adriandingleschemistrypages.com/ap/summary-of-additions-to-new-ap-chemistry-curriculum-part-1-pes/
Electronic
Structure
of Atoms
© 2009, Prentice-Hall, Inc.
PES Example Questions
If the question flagged Mg as the
element in question:
a. Which peak in the spectrum
represents electrons that are closest
to the nucleus?
126 eV
a.
What is the relevance of the relative
height of the peaks at 5.31 and 9.07
eV? different numbers of electrons
a.
Why is there such a large difference
in energy between the peaks at
0.74, 5.31 and 9.07 eV and the peak
at 126 eV? 126 eV – 1s2, biggest
Coulomb effect
From Adrian Dingle’s blog:
http://www.adriandingleschemistrypages.com/ap/summary-of-additions-to-new-ap-chemistry-curriculum-part-1-pes/
Electronic
Structure
of Atoms
© 2009, Prentice-Hall, Inc.
PES Example Questions
If the question did not flag Mg as the
element in question:
a.
Assuming that the PES data shows
ALL the electrons present in the
atom, identify the element.
a.
Still applying the assumption above,
which specific electrons are
associated with the peak at 126 eV?
b.
What does a relatively low value of
energy tell you about the relative
position of the electrons within any
atom?
From Adrian Dingle’s blog:
http://www.adriandingleschemistrypages.com/ap/summary-of-additions-to-new-ap-chemistry-curriculum-part-1-pes/
Electronic
Structure
of Atoms
© 2009, Prentice-Hall, Inc.
PES Example Questions
If the question did not flag Mg as the
element in question:
a.
Assuming that the PES data shows
ALL the electrons present in the
atom, identify the element. Mg
a.
Still applying the assumption above,
which specific electrons are
associated with the peak at 126 eV?
1s2 – closest to the nucleus
a.
What does a relatively low value of
energy tell you about the relative
position of the electrons within any
atom?
They are the valence electron(s)
From Adrian Dingle’s blog:
http://www.adriandingleschemistrypages.com/ap/summary-of-additions-to-new-ap-chemistry-curriculum-part-1-pes/
Electronic
Structure
of Atoms
© 2009, Prentice-Hall, Inc.
PES Example Questions
Mg is found in group 2 and period 3 of
the periodic table. Use this information
to answer the following questions:
a. Predict the full electronic
configuration of Mg using s,p,d,f
notation.
b. Use your answer in a to predict the
relative heights of the four peaks
found in the PES plot for Mg.
From Adrian Dingle’s blog:
http://www.adriandingleschemistrypages.com/ap/summary-of-additions-to-new-ap-chemistry-curriculum-part-1-pes/
Electronic
Structure
of Atoms
© 2009, Prentice-Hall, Inc.
PES Example Questions
Mg is found in group 2 and period 3 of
the periodic table. Use this information
to answer the following questions:
a. Predict the full electronic
configuration of Mg using s,p,d,f
notation.
1s22s22p63s2
a. Use your answer in (a) to predict the
relative heights of the four peaks
found in the PES plot for Mg.
1s2, 2s2 and 3s2 peaks will be the
same height. 2p6 peak will be about
3X higher.
From Adrian Dingle’s blog:
http://www.adriandingleschemistrypages.com/ap/summary-of-additions-to-new-ap-chemistry-curriculum-part-1-pes/
Electronic
Structure
of Atoms
© 2009, Prentice-Hall, Inc.
Recommended Supplemental
PES Material
Coulomb’s Law and AP Chem:
Paul Andersen http://www.bozemanscience.com/apchem-004-coulombs-law/
PES in more depth: UC-Davis Chemwiki
http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectr
oscopy/Photoelectron_Spectroscopy/Photoelectron_Sp
ectroscopy%3A_Theory
Electronic
Structure
of Atoms
© 2009, Prentice-Hall, Inc.