Unit 2: Atoms and Bonding 2.66 Photoelectron Spectroscopy (PES) Not found in Textbook

Big Idea 1: The chemical elements are fundamental building materials of matter, and all matter can be understood in terms of arrangements of atoms. These atoms retain their identity in chemical reactions. Students will be able to demonstrate understanding by laboratory investigation, analysis of data and creation of models. SWBAT: Infer and describe the electronic structure of atoms with multiple electrons from evidence provided by PES data. Interpret Photoelectron Spectroscopy data to determine the binding energy of electrons in an atom or molecule, including those electrons located in core shells. Learning Objectives :

Review: The Photoelectric Effect When light is shone on a substance, the energy from the photons of light excite electrons in the substance. If the energy exceeds the ionization energy of an atom in the substance, the electron is emitted. The emitted electrons are called photoelectrons.

Photoelectron Spectroscopy PES: using the energy from electrons emitted via the photoelectric effect to gain information about the electronic structure of a substance. 2 types: –Photoelectron spectroscopy generally used for the technique when applied to gases, – Photoemission spectroscopy generally used for electrons emitted from solid surfaces.

Interpreting PES Analysis of PES for a single element with a relatively low atomic number is straightforward. This plot is for lithium: 2s 1s

X-axis = binding energy of the electron in electron- volts (eV). Electrons in higher (outer) sublevels are easier to remove so bonding energy is low Peak at the left corresponds with the easiest-to-remove electrons or electrons farther form nucleus (Lithium, its the 2s electron). The peak at the right corresponds with the electrons that are hardest to remove or closer to nucleus (for lithium, it’s the two 1s electrons). 2s 1s

y-axis = number of photons emitted with that energy. Height of each peak is proportional to the number of electrons in the corresponding sub-level. Notice that the peak at 6.26 eV (the 1s electrons) is twice as high as the peak at 0.52 eV (the 2s electron). This means there are twice as many electrons in the 1s sublevel as in the 2s sublevel. The only element that matches this spectrum is lithium (1s 2 2s 1 ).

Problem: Identify the element represented by the following photoelectron spectrum:

References APCentral.collegeboard.com Jennifer K. Howell & Jennifer Pitt-- ‐ Lainsbury for