University:
Morehouse College
Course:
HPHY 253 | Electricity and Magnetism
Academic year:

2021
Views:

118

Pages:

17
Author:

Clint W.

Coulomb’s Law F = attractive/repulsive force Q1 , Q2 = charges (size) r = distance between charges • Is the force between electrons and the nucleus an attraction or a repulsion? It is an attraction • What happens to the force of attraction between the nucleus and an electron as the atoms get larger and there are more and more protons in the nucleus of the atom? • When Q1 or Q2 or both get larger, the attractive force increases • What happens to the force of attraction if the distance between the nucleus and the electron gets larger? • As the charges get farther apart the attractive force between them gets smaller • Based on these answers electrons in which energy level should be held most tightly by the nucleus? • n=1 • Based on these answers, electrons in which orbital within the energy level should be held most tightly by the nucleus? Most loosely? • “s” electrons should be held most tightly • Electrons in the last orbital WITHIN AN ENERGY LEVEL being filled should be held most loosely Photoelectron Spectroscopy • PES apparatus: iramis.cea.fr Photoelectron Spectroscopy How it works: 1. Sample is exposed to EM radiation 2. Electrons jump out of sample and go through analyzer http://chemwiki.ucdavis.edu Image source: Inna M Vishik http://www.stanford.edu/~ivishik/inna_vishik_files/Page452.htm Kinetic Energy Analyzer X-ray or UV Source 6.26 0.52 Binding Energy (MJ/mol) 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ PES Data for Neon Relative Number of Electrons Photo Electron Spectra Each peak represents the electrons in a single sublevel in the atom The bigger the peak , the more electrons 0.1 1 10 100 Energy Electrons generally farther from the nucleus Energy to remove an electron “binding energy” a.k.a ionization energy often measured in eV (electron volts) 1 eV = 1.60217657 × 10-19 J Electrons generally closer to the nucleus Hydrogen vs. Helium Relative Number of Electrons Photo Electron Spectra 0.1 1 Energy 10 The helium peak is farther to the right (higher energy) thus more energy is needed to remove the 1s electrons in helium. They must be held more tightly because there is a higher effective nuclear charge. (Helium has 2 protons pulling on 1s but hydrogen only has 1) The helium peak is twice as tall because there are twice as many electrons in the 1s sublevel Oxygen (1s22s22p4) Relative Number of Electrons Photo Electron Spectra 0.1 1 10 100 Energy 4 electrons in 2p 2 electrons in 2s 2 electrons in 1s Scandium (1s22s22p63s23p64s23d1) Relative Number of Electrons Photo Electron Spectra 0.1 1 10 Energy 100 1000 *Notice that it takes more energy to remove an electron from 3d than from 4s. This is because as electrons are added to 3d they shield 4s thus it’s easier (takes less energy) to remove 4s electrons compared to 3d electrons. Remember when transition metals make positive ions - it’s the s electrons that are lost first! Sodium Why is one peak much Larger than the others? •This peak represents 6 electrons in the 2p sublevel •The other peaks represent only 1 or 2 electrons Relative Number of Electrons Ex1: Identify the element whose PES data is shown 0.1 In which sublevel are the electrons Represented by peak A? 3s Photo Electron Spectra A 1 10 Energy 100 1000 Example 2: oxygen nitrogen #e- #e- energy energy The PES data above shows only the peak for the 1s electrons. Why is the peak for Nitrogen farther to the left? It takes less energy to remove a 1s electron from nitrogen because it has a lower effective nuclear charge (fewer protons) than oxygen Ex3: Sketch the expected PES spectrum for Aluminum Relative Number of Electrons Photo Electron Spectra 0.1 1 10 Energy 100 1000

Phys Photoelectron Spectroscopy

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