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. CHEMISTRY & YOU What makes the electron configuration of an atom stable? Energy and stability play an important role in determining how electrons are configured in an atom.

3. 5.2 Electron Arrangement in Atoms > 3 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. What are the three rules for writing the electron configurations of elements? Electron Configurations

4. 5.2 Electron Arrangement in Atoms > 4 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

5. 5.2 Electron Arrangement in Atoms > 5 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

6. 5.2 Electron Arrangement in Atoms > 6 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

7. 5.2 Electron Arrangement in Atoms > 7 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.

8. 5.2 Electron Arrangement in Atoms > 8 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.

9. 5.2 Electron Arrangement in Atoms > 9 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

10. 5.2 Electron Arrangement in Atoms > 10 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; that is, the electron spins must be paired. Electron Configurations

11. 5.2 Electron Arrangement in Atoms > 11 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

12. 5.2 Electron Arrangement in Atoms > 12 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

13. 5.2 Electron Arrangement in Atoms > 13 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

14. 5.2 Electron Arrangement in Atoms > 14 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

15. 5.2 Electron Arrangement in Atoms > 15 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

16. 5.2 Electron Arrangement in Atoms > 16 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Hund’s Rule Three electrons would occupy three orbitals of equal energy as follows. Electrons then occupy each orbital so that their spins are paired with the first electron in the orbital. Electron Configurations

17. 5.2 Electron Arrangement in Atoms > 17 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.

18. 5.2 Electron Arrangement in Atoms > 18 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.

19. 5.2 Electron Arrangement in Atoms > 19 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.

20. 5.2 Electron Arrangement in Atoms > 20 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

21. 5.2 Electron Arrangement in Atoms > 21 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. A convenient shorthand 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

22. 5.2 Electron Arrangement in Atoms > 22 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. A convenient shorthand 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

23. 5.2 Electron Arrangement in Atoms > 23 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

24. 5.2 Electron Arrangement in Atoms > 24 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

25. 5.2 Electron Arrangement in Atoms > 25 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 that the sum of the superscripts equals the number of electrons in the atom.

26. 5.2 Electron Arrangement in Atoms > 26 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. CHEMISTRY & YOU 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.

27. 5.2 Electron Arrangement in Atoms > 27 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. CHEMISTRY & YOU 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.

28. 5.2 Electron Arrangement in Atoms > 28 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Sample Problem 5.1 Writing Electron Configurations The atomic number of phosphorus is 15. Write the electron configuration of a phosphorus atom.

29. 5.2 Electron Arrangement in Atoms > 29 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Sample Problem 5.1 Analyze Identify the relevant concepts. Phosphorus has 15 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.

30. 5.2 Electron Arrangement in Atoms > 30 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Sample Problem 5.1 SolveApply the concepts to this problem. Use the aufbau diagram to place electrons in the orbital with the lowest energy (1s) first. 2 1s1s

31. 5.2 Electron Arrangement in Atoms > 31 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Sample Problem 5.1 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

32. 5.2 Electron Arrangement in Atoms > 32 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Sample Problem 5.1 The electron configuration of phosphorus is 1s 2 2s 2 2p 6 3s 2 3p 3. The superscripts add up to the number of electrons. 2 SolveApply the concepts to this problem. Write the electron configuration.

33. 5.2 Electron Arrangement in Atoms > 33 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.

34. 5.2 Electron Arrangement in Atoms > 34 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 were to continue in that fashion, however, 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

35. 5.2 Electron Arrangement in Atoms > 35 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

36. 5.2 Electron Arrangement in Atoms > 36 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 although half-filled sublevels are not as stable as filled sublevels, they are more stable than other configurations. Electron Configurations

37. 5.2 Electron Arrangement in Atoms > 37 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

38. 5.2 Electron Arrangement in Atoms > 38 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

39. 5.2 Electron Arrangement in Atoms > 39 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Key Concept Three rules—the aufbau principle, the Pauli exclusion principle, and Hund’s rule—tell you how to find the electron configurations of atoms.

40. 5.2 Electron Arrangement in Atoms > 40 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Glossary Terms electron configuration: the arrangement of electrons of an atom in its ground state into various orbitals around the nuclei of atoms aufbau principle: the rule that electrons occupy the orbitals of lowest energy first Pauli exclusion principle: an atomic orbital may describe at most two electrons, each with opposite spin direction

41. 5.2 Electron Arrangement in Atoms > 41 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Glossary Terms spin: a quantum mechanical property of electrons; it may be thought of as clockwise or counterclockwise 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

42. 5.2 Electron Arrangement in Atoms > 42 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. END OF 5.2