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Chapter 5: Electrons In Atoms

Chapter 5: Electrons In Atoms

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Chapter 5: Electrons In Atoms

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  1. Chapter 5: Electrons In Atoms

  2. Wave Nature of Light • Electromagnetic Radiation – form of energy that exhibits wavelike behaviors as it travels through space • Ex: visible light, microwaves, x-rays, radio, etc.

  3. Wavelength • Symbol – λ (lambda) • Defn – distance between equivalent points on a curve λ λ λ

  4. Frequency • Symbol – f • Defn – number of waves that pass a given point in a second • Unit: Hertz (Hz) • Ex: 300 Hz = 300 1/s = 300 s-1 = 1/s = s-1

  5. Amplitude • Defn – wave’s height from origin to crest crest amplitude origin

  6. Electromagnetic Waves • All EM waves travels at the speed of light (c) • c = 3 x 108 m/s • c = (wavelength)(frequency) c = λf = 3 x 108 m/s

  7. Wavelength and Frequency Relationship • Inversely related: as one increases, other decreases shortλ high frequency longλ low frequency

  8. Electromagnetic Spectrum • Defn – shows all forms of electromagnetic radiation

  9. Ex problem #1 • What is the wavelength of a microwave with a frequency of 3.44 x 109 s-1? c = λf c 3 x108 m/s 8.72 x 10-2 m = λ = = 3.44 x 109 s-1 f

  10. Ex problem #2 • What is the frequency of green light, which has a wavelength of 4.90 x 10-7 m? c = λf c 3 x108 m/s = = f = 4.90 x 10-7 m λ 6.12 x 1014 Hz

  11. Particle Nature of Light • Quantum – minimum amount of energy that can be gained or lost by an atom • Photoelectric Effect – emission of electrons from metal’s surface when light of specific frequency shines on surface light e- METAL

  12. Photon – particle of light • Photon Energy • Unit: joules (J) • formula Ephoton = hf h = Planck’s constant = 6.626 x 10-34 J·s f = frequency (s-1)

  13. Ex problem • What is the energy of a photon from the violet portion of the rainbow if it has a frequency of 7.23 x 1014 s-1? E = hf = (6.626 x 10-34 J·s) (7.23 x 1014 s-1) = 4.79 x 10-19 J

  14. Bohr Model of an Atom • Ground State – lowest energy state of an atom • Excited State – state when atom gains energy **pay attention to the electrons** • Bohr Model – shows electron orbit and energy level of an electron

  15. Bohr Model E1 = lowest energy level E3 > E2 > E1 E1 E2 E3

  16. in ground state, no energy radiated in excited state, electrons jump to higher energy level electron go from high E level to low E level photon emitted Ground State to Excited State 4 6 1) 5 4 2) 3 3 2 Energy of atom 2 3) 1 4) 1

  17. Atomic Orbitals • Defn – 3D region around nucleus describing specific electron’s location

  18. Principle Quantum Number (n) • Defn – indicates the energy level an electron is on - use periodic table to tell (look at rows) n = 1,2,3,…..

  19. Principal Quantum Number

  20. Energy Sublevels/Orbitals • Defn – shape of orbital that tells the path of the electrons • 4 sublevels: s, p, d, f Let’s focus on the s and p orbitals

  21. s orbital • Shape: electrons travel in a sphere

  22. s orbital 3s 1s 2s The greater the energy level, the bigger the orbital

  23. p orbital • Shape: dumbbell or figure 8 shaped

  24. Electron Configuration • Defn – arrangement of electrons in an atom Where are certain electrons located?

  25. Rules Governing Electron Configurations 1) Aufbau Principle – electrons occupy lowest energy orbital available - fill up level 1 first, then level 2, etc. 2) Pauli Exclusion Principle – there is a max number of electrons that occupy a single orbital (2)

  26. Rules Governing Electron Configurations 3) Hund’s Rule – if orbitals have equal energy, one e- will go in each orbital before doubling up 1 2 3 5 6 4

  27. Blocks On Periodic Table s s p d f

  28. Divisions of Orbitals • s orbital – 1 sublevel (2 e- max) • p orbital – 3 sublevels (6 e- max) • d orbital – 5 sublevels (10 e- max) • f orbital – 7 sublevels (14 e- max)

  29. Orbital Diagram • Nitrogen • How many electrons? • What energy level is nitrogen on? 7 n = 2 1s 2s 2p

  30. Orbital Diagram • Silicon • How many electrons? • What energy level is silicon on? 14 n = 3 1s 2s 2p 3s 3p

  31. Orbital Diagram • Copper • How many electrons? • What energy level is copper on? 29 n = 4 1s 2s 2p 3s 3p 4s 3d

  32. Electron Configuration Notation 2 2 4 • Oxygen (8 e-) • Sulfur (16 e-) • Vanadium (23 e-) • Zirconium (40 e-) 2s 2p 1s 2 2 6 2 4 2s 2p 3s 3p 1s 2 2 6 2 6 2 3 2s 2p 3s 3p 4s 3d 1s 2 2 6 2 6 2 10 6 2 2 2s 2p 3s 3p 4s 3d 4p 5s 4d 1s

  33. Noble Gas Notation • Rule: start from previous noble gas, then write the configuration • Oxygen • Sulfur • Vanadium • Zirconium 2 4 [He] 2s 2p 2 4 [Ne] 3s 3p 2 3 [Ar] 4s 3d 2 2 [Kr] 5s 4d

  34. Valence Electrons • defn – electrons in outer most energy level - located in highest s & p orbitals (max 8) N: Mg: Se: 2 2 3 5 valence e- 1s 2s 2p 2 2 6 2 2 valence e- 1s 2s 2p 3s 2 2 6 2 6 2 10 4 1s 2s 2p 3s 3p 4s 3d 4p 6 valence e-

  35. Electron Dot Structure • Defn – shows number of valence e- by diagram • Nitrogen (5 v.e.) • Magnesium (2 v.e.) • Selenium (6 v.e.) N Mg Se