1. 5.2 Electron Arrangement in Atoms > 1 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Chapter 5 Electrons In Atoms 5.1 Revising the Atomic Model 5.2 Electron Arrangement in Atoms 5.3 Atomic Emission Spectra and the Quantum Mechanical Model

2. 5.2 Electron Arrangement in Atoms > 2 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. What gives gas-filled lights their colors? An electric current passing through the gas in each glass tube makes the gas glow with its own characteristic color. CHEMISTRY & YOU

3. 5.2 Electron Arrangement in Atoms > 3 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Light and Atomic Emission Spectra What causes atomic emission spectra?

4. 5.2 Electron Arrangement in Atoms > 4 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. When atoms absorb energy, their electrons move to higher energy levels. These electrons lose energy, by emitting light, when they return to their original (ground) energy levels. Light and Atomic Emission Spectra Atomic Emission Spectra

5. 5.2 Electron Arrangement in Atoms > 5 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. A prism separates light into the colors it contains. White light produces a rainbow of colors. Light and Atomic Emission Spectra Light bulb SlitPrism Screen Atomic Emission Spectra

6. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Light from a helium lamp produces discrete lines. Light and Atomic Emission Spectra SlitPrism Screen Helium lamp Atomic Emission Spectra

7. 5.2 Electron Arrangement in Atoms > 7 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. An Explanation of Atomic Spectra How is the color of light emitted by an atom related to changes of electron energies?

8. 5.2 Electron Arrangement in Atoms > 8 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. An Explanation of Atomic Spectra The light emitted by an electron moving from a higher to a lower energy level has a color directly proportional to the energy change of the electron.

9. 5.2 Electron Arrangement in Atoms > 9 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. An Explanation of Atomic Spectra When an electron has its lowest possible energy, the atom is in its ground state. In the ground state, the principal quantum number (n) is equal to it’s energy level.

10. 5.2 Electron Arrangement in Atoms > 10 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. An Explanation of Atomic Spectra When an electron has its lowest possible energy, the atom is in its ground state. In the ground state, the principal quantum number (n) is equal to it’s energy level. Excitation of the electron by absorbing energy raises the atom to an excited state.

11. 5.2 Electron Arrangement in Atoms > 11 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. An Explanation of Atomic Spectra When an electron has its lowest possible energy, the atom is in its ground state. In the ground state, the principal quantum number (n) is equal to it’s energy level. Excitation of the electron by absorbing energy raises the atom to an excited state. A quantum of energy in the form of light is emitted when the electron drops back to a lower energy level.

12. An Explanation of Atomic Spectra Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

13. 5.2 Electron Arrangement in Atoms > 13 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. The energy absorbed by an electron is identical to the energy of the light emitted by the electron as it drops back to its original energy level. Light and Atomic Emission Spectra Atomic Emission Spectra

14. 5.2 Electron Arrangement in Atoms > 14 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. The energy absorbed by an electron is identical to the energy of the light emitted by the electron as it drops back to its original energy level. The wavelengths of the spectral lines are characteristic of the element, and they make up the atomic emission spectrum of the element. Light and Atomic Emission Spectra Atomic Emission Spectra

15. 5.2 Electron Arrangement in Atoms > 15 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. The energy absorbed by an electron is identical to the energy of the light emitted by the electron as it drops back to its original energy level. The wavelengths of the spectral lines are characteristic of the element, and they make up the atomic emission spectrum of the element. No two elements have the same emission spectrum. Light and Atomic Emission Spectra Atomic Emission Spectra

16. 5.2 Electron Arrangement in Atoms > 16 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. CHEMISTRY & YOU What makes the electron configuration of an atom stable? Having a completely filled valence level. Energy and stability play an important role in determining how electrons are configured in an atom.

17. 5.2 Electron Arrangement in Atoms > 17 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. What are the three rules for writing the electron configurations of elements? Electron Configurations

18. 5.2 Electron Arrangement in Atoms > 18 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Three rules—the aufbau principle, the Pauli exclusion principle, and Hund’s rule—tell you how to find the electron configurations of atoms. Electron Configurations

19. 5.2 Electron Arrangement in Atoms > 19 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. The ways in which electrons are arranged in various orbitals around the nuclei of atoms are called electron configurations. Electron Configurations

20. 5.2 Electron Arrangement in Atoms > 20 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Aufbau Principle Electron Configurations According to the aufbau principle, electrons occupy the orbitals of lowest energy first. In the aufbau diagram, each box represents an atomic orbital. Increasing energy 6s6s 5s5s 4s4s 3s3s 2s2s 1s1s 6p6p 5p5p 5d5d 4p4p 4d4d 4f4f 3p3p 3d3d 2p2p

21. 5.2 Electron Arrangement in Atoms > 21 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Aufbau Principle Electron Configurations Increasing energy 6s6s 5s5s 4s4s 3s3s 2s2s 1s1s 6p6p 5p5p 5d5d 4p4p 4d4d 4f4f 3p3p 3d3d 2p2p The aufbau diagram shows the relative energy levels of the various atomic orbitals. Orbitals of greater energy are higher on the diagram.

22. 5.2 Electron Arrangement in Atoms > 22 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Aufbau Principle Electron Configurations Increasing energy 6s6s 5s5s 4s4s 3s3s 2s2s 1s1s 6p6p 5p5p 5d5d 4p4p 4d4d 4f4f 3p3p 3d3d 2p2p The range of energy levels within a principal energy level can overlap the energy levels of another principal level.

23. 5.2 Electron Arrangement in Atoms > 23 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Pauli Exclusion Principle According to the Pauli exclusion principle, an atomic orbital may describe at most two electrons. Electron Configurations

24. 5.2 Electron Arrangement in Atoms > 24 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Pauli Exclusion Principle According to the Pauli exclusion principle, an atomic orbital may describe at most two electrons. To occupy the same orbital, two electrons must have opposite spins. Electron Configurations

25. 5.2 Electron Arrangement in Atoms > 25 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Pauli Exclusion Principle According to the Pauli exclusion principle, an atomic orbital may describe at most two electrons. To occupy the same orbital, two electrons must have opposite spins. The electron spins must be paired to fill the orbital. Electron Configurations

26. 5.2 Electron Arrangement in Atoms > 26 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Pauli Exclusion Principle Spin is a quantum mechanical property of electrons and may be thought of as clockwise or counterclockwise. Electron Configurations

27. 5.2 Electron Arrangement in Atoms > 27 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Pauli Exclusion Principle Spin is a quantum mechanical property of electrons and may be thought of as clockwise or counterclockwise. A vertical arrow indicates an electron and its direction of spin (  or  ). Electron Configurations

28. 5.2 Electron Arrangement in Atoms > 28 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Pauli Exclusion Principle Spin is a quantum mechanical property of electrons and may be thought of as clockwise or counterclockwise. A vertical arrow indicates an electron and its direction of spin (  or  ). An orbital containing paired electrons is written as. Electron Configurations

29. 5.2 Electron Arrangement in Atoms > 29 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Hund’s Rule According to Hund’s rule, electrons occupy orbitals of the same energy in a way that makes the number of electrons with the same spin direction as large as possible. Electron Configurations

30. 5.2 Electron Arrangement in Atoms > 30 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Hund’s Rule Three electrons would occupy three orbitals of equal energy as follows. Electron Configurations

31. 5.2 Electron Arrangement in Atoms > 31 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Hund’s Rule Three electrons would occupy three orbitals of equal energy as follows. If more electrons are needing to be placed in those orbitals, then they would be paired starting with the electron in the first orbital. Electron Configurations

32. 5.2 Electron Arrangement in Atoms > 32 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Electron Configurations Look at the orbital filling diagram of the oxygen atom. Electron Configurations of Selected Elements Element1s1s2s2s2p x 2p y 2p z 3s3s Electron configuration H1s11s1 He1s21s2 Li1s22s11s22s1 C1s22s22p21s22s22p2 N1s22s22p31s22s22p3 O1s22s22p41s22s22p4 F1s22s22p51s22s22p5 Ne1s22s22p61s22s22p6 Na1s22s22p63s11s22s22p63s1 An oxygen atom contains eight electrons.

33. 5.2 Electron Arrangement in Atoms > 33 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Electron Configurations Look at the orbital filling diagram of the oxygen atom. Electron Configurations of Selected Elements Element1s1s2s2s2p x 2p y 2p z 3s3s Electron configuration H1s11s1 He1s21s2 Li1s22s11s22s1 C1s22s22p21s22s22p2 N1s22s22p31s22s22p3 O1s22s22p41s22s22p4 F1s22s22p51s22s22p5 Ne1s22s22p61s22s22p6 Na1s22s22p63s11s22s22p63s1 The 1s orbital has two electrons of opposite spin.

34. 5.2 Electron Arrangement in Atoms > 34 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Electron Configurations Look at the orbital filling diagram of the oxygen atom. Electron Configurations of Selected Elements Element1s1s2s2s2p x 2p y 2p z 3s3s Electron configuration H1s11s1 He1s21s2 Li1s22s11s22s1 C1s22s22p21s22s22p2 N1s22s22p31s22s22p3 O1s22s22p41s22s22p4 F1s22s22p51s22s22p5 Ne1s22s22p61s22s22p6 Na1s22s22p63s11s22s22p63s1 The 1s orbital has two electrons of opposite spin. The 2s orbital also has two electrons of opposite spin.

35. 5.2 Electron Arrangement in Atoms > 35 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Electron Configurations Look at the orbital filling diagram of the oxygen atom. Each of the three 2p orbitals has one electron. The remaining electron now pairs with an electron occupying one of the 2p orbitals. Electron Configurations of Selected Elements Element1s1s2s2s2p x 2p y 2p z 3s3s Electron configuration H1s11s1 He1s21s2 Li1s22s11s22s1 C1s22s22p21s22s22p2 N1s22s22p31s22s22p3 O1s22s22p41s22s22p4 F1s22s22p51s22s22p5 Ne1s22s22p61s22s22p6 Na1s22s22p63s11s22s22p63s1

36. 5.2 Electron Arrangement in Atoms > 36 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. A method for showing the electron configuration of an atom involves writing the energy level and the symbol for every sublevel occupied by an electron. Electron Configurations

37. 5.2 Electron Arrangement in Atoms > 37 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. A method for showing the electron configuration of an atom involves writing the energy level and the symbol for every sublevel occupied by an electron. You indicate the number of electrons occupying that sublevel with a superscript. Electron Configurations

38. 5.2 Electron Arrangement in Atoms > 38 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. For hydrogen, with one electron in a 1s orbital, the electron configuration is written 1s 1. Electron Configurations

39. 5.2 Electron Arrangement in Atoms > 39 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. For hydrogen, with one electron in a 1s orbital, the electron configuration is written 1s 1. For oxygen, with two electrons in a 1s orbital, two electrons in a 2s orbital, and four electrons in 2p orbitals, the electron configuration is 1s 2 2s 2 2p 4. Electron Configurations

40. 5.2 Electron Arrangement in Atoms > 40 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. For hydrogen, with one electron in a 1s orbital, the electron configuration is written 1s 1. For oxygen, with two electrons in a 1s orbital, two electrons in a 2s orbital, and four electrons in 2p orbitals, the electron configuration is 1s 2 2s 2 2p 4. Electron Configurations Note: The sum of the superscripts equals the number of electrons in the atom.

41. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Explain why the correct electron configuration of oxygen is 1s 2 2s 2 2p 4 and not 1s 2 2s 2 2p 3 3s 1.

42. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Explain why the correct electron configuration of oxygen is 1s 2 2s 2 2p 4 and not 1s 2 2s 2 2p 3 3s 1. The 2p orbitals are lower in energy than the 3s orbital, so they will be completely filled before any electrons will be found in the 3s orbital.

43. 5.2 Electron Arrangement in Atoms > 43 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Sample Problem Writing Electron Configurations The atomic number of chlorine is 17. Write the electron configuration of a chlorine atom.

44. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Sample Problem Analyze Identify the relevant concepts. Chlorine has 17 electrons. There is a maximum of two electrons per orbital. Electrons do not pair up within an energy sublevel (orbitals of equal energy) until each orbital already has one electron. 1 When writing electron configurations, the sublevels within the same principal energy level are written together.

45. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Sample Problem SolveApply the concepts to this problem. Use the aufbau diagram to place electrons in the orbital with the lowest energy (1s) first. 2 1s1s2s2s2p2p3p3p3s3s4s4s

46. 5.2 Electron Arrangement in Atoms > 46 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Sample Problem SolveApply the concepts to this problem. Use the aufbau diagram to place electrons in the orbital with the lowest energy (1s) first. Continue placing electrons in each orbital with the next higher energy level. 2 1s1s2s2s2p2p3p3p3s3s4s4s

47. 5.2 Electron Arrangement in Atoms > 47 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Sample Problem SolveApply the concepts to this problem. 2 1s1s2s2s2p2p3p3p3s3s4s4s Write the electron configuration. The electron configuration of chlorine is 1s 2 2s 2 2p 6 3s 2 3p 5. The superscripts add up to the number of electrons found in a chlorine atom (17).

48. 5.2 Electron Arrangement in Atoms > 48 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Exceptional Electron Configurations Electron Configurations You can obtain correct electron configurations for the elements up to vanadium (atomic number 23) by following the aufbau diagram for orbital filling.

49. 5.2 Electron Arrangement in Atoms > 49 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Exceptional Electron Configurations You can obtain correct electron configurations for the elements up to vanadium (atomic number 23) by following the aufbau diagram for orbital filling. If you continued, you would assign chromium and copper the following incorrect configurations. Cr 1s 2 2s 2 2p 6 3s 2 3p 6 3d 4 4s 2 Cu 1s 2 2s 2 2p 6 3s 2 3p 6 3d 9 4s 2 Electron Configurations Cr 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 4 Cu 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 9 or newold

50. 5.2 Electron Arrangement in Atoms > 50 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Exceptional Electron Configurations The correct electron configurations are as follows: Cr 1s 2 2s 2 2p 6 3s 2 3p 6 3d 5 4s 1 Cu 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 1 These arrangements give chromium a half-filled d sublevel and copper a filled d sublevel. Electron Configurations Cr 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 5 Cu 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 10 or newold

51. 5.2 Electron Arrangement in Atoms > 51 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Exceptional Electron Configurations Some actual electron configurations differ from those assigned using the aufbau principle because half-filled sublevels are not as stable as filled sublevels, but are more stable than other configurations. Electron Configurations

52. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. What is the correct electron configuration of a sulfur atom? A. 1s 2 2s 2 2p 4 3s 2 3p 6 B. 1s 2 2s 2 2p 6 3s 2 3p 3 C. 1s 2 2s 2 2p 6 3s 2 3p 4 D. 1s 2 2s 2 2p 6 3s 6 3p 2

53. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. What is the correct electron configuration of a sulfur atom? A. 1s 2 2s 2 2p 4 3s 2 3p 6 B. 1s 2 2s 2 2p 6 3s 2 3p 3 C. 1s 2 2s 2 2p 6 3s 2 3p 4 D. 1s 2 2s 2 2p 6 3s 6 3p 2

54. 5.2 Electron Arrangement in Atoms > 54 [ ] Shorthand Method to Electron Configuration 1.) Write the chemical symbol of the Noble gas at the end of the row above the one containing the element you are working on. 2.) Place brackets [ ] around that symbol. 3.) Write the electron configuration for the last row containing the element you are working on. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Electron Configurations ex.: manganese Ar 4s 2 3d 5 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 5

55. 5.2 Electron Arrangement in Atoms > 55 Every electron has four (4) quantum numbers assigned to it. The Pauli Exclusion Principle says “No two electrons can have the exact same quantum numbers.” 1.) The first number is the principle quantum number and corresponds to the electron’s energy level. (n) 2.) The second number is the angular momentum {azimuthal} and corresponds to the orbital shape. (ℓ) 3.) The third number is the magnetic and corresponds to the orbital order or sequence. (m ℓ ) 4.) The fourth number is the spin and corresponds to the direction of motion (clockwise or counter clockwise). (m s ) Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Electron Configurations

56. 5.2 Electron Arrangement in Atoms > 56 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Electron Configurations Summary of Quantum Numbers and Orbital Designations 1.) Principal Energy Level (n) 2.) Angular Momentum (Azimuthal) (ℓ) 3.) Magnetic (m ℓ ) 4.) Spin (m s ) Maximum Number of Electrons 100± ½2 2 0101 0 -1, 0, +1 ± ½ 8 3 012012 0 -1, 0, +1 -2, -1, 0, +1, +2 ± ½ 18 4 01230123 0 -1, 0, +1 -2, -1, 0, +1, +2 -3, -2, -1, 0, +1, +2, +3 ± ½ 32 Quantum numbers assigned to electrons.

57. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. What are the four (4) quantum numbers associated with manganese.

58. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. What are the four (4) quantum numbers associated with manganese. n = 4 ℓ = 2 m ℓ = +2 m s = +½

59. 5.2 Electron Arrangement in Atoms > 59 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. When atoms absorb energy, their electrons move to higher energy levels. These electrons lose energy by emitting light when they return to lower energy levels. The light emitted by an electron moving from a higher to a lower energy level has a color directly proportional to the energy change of the electron. Three rules—the aufbau principle, the Pauli exclusion principle, and Hund’s rule—tell you how to find the electron configurations of atoms. Key Concepts and Key Equations

60. 5.2 Electron Arrangement in Atoms > 60 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. END OF 5.2