Spectroscopy © 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) © 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 © 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 © 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 for details © 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. © 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 © 2009, Prentice-Hall, Inc.

Example of PES What does this mean? 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/ © 2009, Prentice-Hall, Inc.

PES Example Questions If the question flagged Mg as the element in question: Which peak in the spectrum represents electrons that are closest to the nucleus? What is the relevance of the relative height of the peaks at 5.31 and 9.07 eV? 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/ © 2009, Prentice-Hall, Inc.

PES Example Questions If the question flagged Mg as the element in question: Which peak in the spectrum represents electrons that are closest to the nucleus? 126 eV What is the relevance of the relative height of the peaks at 5.31 and 9.07 eV? different numbers of electrons 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/ © 2009, Prentice-Hall, Inc.

PES Example Questions If the question did not flag Mg as the element in question: Assuming that the PES data shows ALL the electrons present in the atom, identify the element. Still applying the assumption above, which specific electrons are associated with the peak at 126 eV? 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/ © 2009, Prentice-Hall, Inc.

PES Example Questions If the question did not flag Mg as the element in question: Assuming that the PES data shows ALL the electrons present in the atom, identify the element. Mg Still applying the assumption above, which specific electrons are associated with the peak at 126 eV? 1s2 – closest to the nucleus 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/ © 2009, Prentice-Hall, Inc.

From Adrian Dingle’s blog: PES Example Questions Mg is found in group 2 and period 3 of the periodic table. Use this information to answer the following questions: Predict the full electronic configuration of Mg using s,p,d,f notation. 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/ © 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: Predict the full electronic configuration of Mg using s,p,d,f notation. 1s22s22p63s2 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/ © 2009, Prentice-Hall, Inc.

Recommended Supplemental PES Material Coulomb’s Law and AP Chem: Paul Andersen http://www.bozemanscience.com/ap-chem-004-coulombs-law/ PES in more depth: UC-Davis Chemwiki http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Photoelectron_Spectroscopy/Photoelectron_Spectroscopy%3A_Theory © 2009, Prentice-Hall, Inc.