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Chapter 7; Electronic Structure of Atoms

Chapter 7; Electronic Structure of Atoms. Electromagnetic Radiation Flame Test/ Emission Spectra Quantized Energy Levels Bohr Model/ Rydberg Equation Principal Energy Levels, n First Ionization Energy 2 nd , 3 rd , 4 th , etc Ionization Energy. Chapter 7; Electronic Structure of Atoms.

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Chapter 7; Electronic Structure of Atoms

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  1. Chapter 7; Electronic Structure of Atoms • Electromagnetic Radiation • Flame Test/ Emission Spectra • Quantized Energy Levels • Bohr Model/ Rydberg Equation • Principal Energy Levels, n • First Ionization Energy • 2nd , 3rd, 4th, etc Ionization Energy

  2. Chapter 7; Electronic Structureof Atoms • Sublevels (s, p, d, f) • Photoelectron Spectroscopy • Electron Configuration • Valence Electrons/ Core • Good/ Bad Point of Atom Model • Quantum Theory • Dual Nature of the Electron • Heisenberg Uncertainty Principle

  3. Chapter 7; ElectronicStructure of Atoms • Quantum Numbers (n, l, ml, ms) • Oribtal Diagrams • Paramagnetism and Diamagnetism

  4. Wave Properties Frequency (n) is the number of waves that pass through a particular point in 1 second (Hz = 1 cycle/s) All waves travel through space at same rate; c • C= 3.00 X108 m/s

  5. Higher frequency (); Lower wavelength Higher Energy Wave Properties

  6. Longer Wavelength Higher Frequency and Energy

  7. Longer Wavelength, Lower Energy

  8. Flame Test for Cations sodium lithium potassium copper 16.11

  9. Light Photon Flame Test • Electron absorbs • energy from the flame • goes to a higher energy • state. 2. Electron goes back down to lower energy state and releases the energy it absorbed as light.

  10. Emission of Energy(2 Possibilities) or Continuous Energy Loss Quantized Energy Loss

  11. Continuous Energy Loss Any and all energy values possible on way down Implies electron can be anywhere about nucleus of atom Continuous emission spectra Quantized Energy Loss Only certain, restricted, quantized energy values possible on way down Implies an electron is restricted to quantized energy levels Line spectra Emission of Energy

  12. Emission Spectrum Line Emission Spectrum (Quantized Energy Loss) Continuous EmissionSpectrum

  13. Line Emission Spectrum of Hydrogen Atoms H2 Emission Spectrum 7.3

  14. Line Spectra vs. Continuous Emission Spectra • The fact that the emission spectra H2 gas and other molecules is a line rather than continuous emission spectra tells us that electrons are in quantized energy levels rather than anywhere about nucleus of atom.

  15. ( ) En = -RH 1 n2 Bohr’s Model of the Atom (1913) • e- can only have specific (quantized) energy values • light is emitted as e- moves from one energy level to a lower energy level n (principal quantum number) = 1,2,3,… RH (Rydberg constant) = 2.18 x 10-18J 7.3

  16. Electronic Structure • Electrons are in Quantized Energy Levels • The maximum number of electrons in principal energy level, n, is 2n2. • Lower energy levels are completely filled before higher energy levels are filled.

  17. Experimental evidence to show the number • of electrons in a principal energy level,n. First Ionization Energy Energy to remove the 1st (or most loosely bond) electron from an atom in the gaseous state. -higher IE, harder to remove e-

  18. Increasing First Ionization Energy Increasing First Ionization Energy First Ionization Energy;(MJ/mole) Harder to remove electron

  19. Factors in First Ionization Energy • Principal Energy Level, n, the Most Loosely Bond Electron is in. • Higher ‘n’- Easier to Remove; Lower IE (Explains Trend Going Down Group) • Charge in the Nucleus of the Atom. • Higher atomic #; Harder to Remove; Higher IE (Explains Trend Going Across Period)

  20. n=1 n=1 +2 +1 He IE = 2.37 H IE = 1.31 The nuclear charge of Helium is twice that of Hydrogen; thus you’d expect the ionization energy for helium to be twice that of hydrogen if the second electron is in the same principal energy level. H vs. He

  21. n=2 n=1 n=1 +3 +1 Li IE = 0.52 H IE = 1.31 • Since the ionization energy of lithium is less than half that of H even though the nuclear charge of Li is 3X more than H; we put the third electron in a higher energy level. • This is how we know principal energy level one contains a maximum of 2 electrons. H vs. Li

  22. n=2 n=1 +3 Li IE = 0.52 Carbon has twice the nuclear charge of lithium and it’s ionization energy is about twice that of lithium. Thus, we know the 4th, 5th, and 6th electron are still in n=2 since the ionization energy has not decreased while the nuclear charge increased. Li vs. C n=2 n=1 +6 C IE = 1.09

  23. The ionization energy still increases while the nuclear charge increases between carbon and neon. This means we are still filling n=2. Ne vs. C n=2 n=2 n=1 n=1 Trend Across Period +10 +6 Ne IE = 2.08 C IE = 1.09

  24. n=3 n=2 n=2 n=1 n=1 +11 +10 Na IE = 0.50 Ne IE = 2.08 • As the 11th electron is added the ionization energy decreases even though the nuclear charge • increases. This means the 11th electron must go in a higher energy level. • This is how we know n=2 holds a maximum of 8 electrons. Ne vs. Na

  25. n=3 n=2 n=2 n=1 n=1 +11 +3 Na IE = 0.50 Li IE = 0.52 Li vs. Na Trend Going Down Group Even though Na has a higher nuclear charge; the ionization energy is lower since the electron is in a higher ‘n.’ Shielding effect Filled principal energy levels shield full effect of positive charge of nucleus

  26. Explaining Trends in Ionization Energy • Determine the number of electrons in each principal energy level. • Look at the principal energy level the most loosely bond electron is in. • Look at the nuclear charge (atomic #)

  27. Experimental Data That Tells How Many Electrons are in Each Principal Energy Level • Trends in the Values of First Ionization Energies for Different Elements. • Trends in the 1st, 2nd, 3rd, 4th, etc Ionization Energy for the Same Element. • Photoelectron Spectroscopy

  28. Ionization Energies (IE) • 1st IE; Energy to remove the 1st (or most loosely bond) electron from an atom in the gaseous state. • 2nd IE; Energy to remove the 2nd most loosely bond electron from an atom in the gaseous state. • 3rd IE; Energy to remove the 3rd most loosely bond electron from an atom in the gaseous state.

  29. Ionization Energies for Selected Elements, kJ/Mole

  30. n=2 n=2 n=1 n=1 n=2 n=1 +3 +3 Li+1 2nd IE = 7300 +3 Li+2 3rd IE = 11815 Li 1st IE = 520 Multiple Ionization Energies for Li 2nd IE is much larger than 1st IE since electron is removed from lower ‘n’ No 4th Ionization Energy; no more electrons

  31. n=2 n=1 +4 Be+1 2nd IE = 1757 Multiple Ionization Energies for Be n=2 n=2 n=1 n=1 +4 +4 Be+2 3rd IE = 14850 Be 1st IE = 899 Big jump in IE means removing electron from lower ‘n’

  32. Multiple Ionization Energies for Be (continued) n=2 n=2 n=1 n=1 +4 +4 Be+2 4th IE = 21005 Be+2 5th IE = NA No 5th IE since only have 4 electrons in Be

  33. n=3 n=3 n=3 n=2 n=2 n=2 n=1 n=1 n=1 +12 +12 +12 Mg+2 3rd IE = 7730 Mg+1 2nd IE = 1450 Big jump between 2nd and 3rd IE since removing electron from lower ‘n’ Multiple Ionization Energies for Mg n=3 n=2 n=1 +12 Mg 1st IE = 738 2nd IE is about 2X 1st IE since removing electron from same ‘n’

  34. n=3 n=3 n=3 n=2 n=2 n=2 n=1 n=1 n=1 +12 +12 +12 Mg+5 6th IE = 18000 Mg+4 5th IE = 13600 Mg+3 4th IE = 10500 Multiple Ionization Energies for Mg (Continued)

  35. There is a big jump between the 2nd and 3rd IE for both Be and Mg since both are removing an electron from a lower ‘n’

  36. Mg always has a lower IE than Be since the electron is always being removed from a higher ‘n.’

  37. Experimental Evidence That Suggests That Principal Energy Levels Have Sublevels Associated With Them • Emission Spectrum • Photoelectron Spectrum

  38. Emission Spectrum for Barium Emission Spectrum for Neon

  39. Photoelectron Spectrum • Peak Area is Proportional to Number of Electrons • Breaks in Ionization Energy Scale Represent Different Energy Levels • Number of Peaks Within Breaks Equals Number of Sublevels Within Principal Energy Level

  40. n=1 +2 He IE = 2.37 Taken from; Chemistry – A Guided Inquiry; by Richard S Moog & John Farrell; John Wiley & Sons, Inc;1999

  41. Taken from; Chemistry – A Guided Inquiry; by Richard S Moog & John Farrell; John Wiley & Sons, Inc;1999 n=2 n=1 +10 Ne IE = 2.08 Old Picture

  42. Taken from; Chemistry – A Guided Inquiry; by Richard S Moog & John Farrell; John Wiley & Sons, Inc;1999 Revised Picture 2p n=2 2p 2s 1s n=1 1s 2s +10 Ne IE = 2.08

  43. Taken from; Chemistry – A Guided Inquiry; by Richard S Moog & John Farrell; John Wiley & Sons, Inc;1999

  44. 2p 1s 2s 3s 3s 2p n=2 2s 1s n=1 + Taken from; Chemistry – A Guided Inquiry; by Richard S Moog & John Farrell; John Wiley & Sons, Inc;1999

  45. Taken from; Chemistry – A Guided Inquiry; by Richard S Moog & John Farrell; John Wiley & Sons, Inc;1999

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