1. Section 8.4 Ions: Electron Configurations and Sizes Return to TOC Electron Configurations in Stable Compounds When two nonmetals react to form a covalent bond, they share electrons in a way that completes the valence electron configurations of both atoms. When a nonmetal and a representative-group metal react to form a binary ionic compound, the ions form so that the valence electron configuration of the nonmetal achieves the electron configuration of the next noble gas atom. The valence orbitals of the metal are emptied. 1

2. Section 8.4 Ions: Electron Configurations and Sizes Return to TOC Ions An ion is an atom with a charge Cation – positively charged atom Anion – negatively charged atom The question becomes….why do atoms form ions? 2

3. Section 8.4 Ions: Electron Configurations and Sizes Return to TOC Ions Atoms will gain or lose e- in an attempt to form the same electron configuration as the closest noble gas. ***Move the LEAST number of e- possible. 3

4. Section 8.4 Ions: Electron Configurations and Sizes Return to TOC Ions Atoms in groups 1 and 2 will lose the outer valence e- first. These are the “s” e- Atoms in groups 13-15, below the “stairs” will lose their outer “p” e- first, then their outer “s” e- Exceptions: B, Al tend to lose both the “p” and “s” e- at the same time 4

5. Section 8.4 Ions: Electron Configurations and Sizes Return to TOC Transition Metals – lose their valence “s” e- first, then they may lose another e- from the “d” sublevel. Exceptions: Ag, Zn, Cd – they do NOT lose e- from the “d” sublevel Why? After they lose their “s” electrons, it takes too much energy to take from the full “d” sublevel 5

6. Section 8.4 Ions: Electron Configurations and Sizes Return to TOC 6 Rules for Filling Orbitals – Any orbital may contain 0, 1, or, at most, 2 electrons. – In filling the p, d, and f subsets, each orbital gets a single electron with the same spin as the others before any pairing takes place. – This is because more energy would be required to fill them in any other way. ELECTRON CONFIGURATIONS

7. Section 8.4 Ions: Electron Configurations and Sizes Return to TOC 7 Elements with atomic numbers 1  4 have only s electrons Elements with atomic numbers 5  10 also have electrons in p orbitals Elements 21  30 have d electrons Elements 58  71 have electrons in f orbitals along with all their other electrons. Figure 3.18, pg. 78 Investigating Chemistry, 2nd Edition © 2009 W.H. Freeman & Company ELECTRON CONFIGURATIONS

8. Section 8.4 Ions: Electron Configurations and Sizes Return to TOC 8 Beryllium has an atomic number of 4, with two 1s electrons and with two electrons in the 2s orbital. Adding the superscripts gives the total number of electrons. ELECTRON CONFIGURATIONS

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10. Note the exceptions in red. Copper, Cu, also has an unexpected configuration. 10

11. Section 8.4 Ions: Electron Configurations and Sizes Return to TOC 11 ELECTRON CONFIGURATIONS It was once suspected that the deposed Emperor Napoleon was poisoned with arsenic. What is the electron configuration of arsenic, As, element number 33? Following the periodic table from H, to He, to Li, Be, B, C, N, O, F, etc., – We get 1s 2, 2s 2, 2p 6, 3s 2, 3p 6 … – So far we have 2 + 2 + 6 + 2 + 6 = 18 e’s.

12. Section 8.4 Ions: Electron Configurations and Sizes Return to TOC 12 1s 2, 2s 2, 2p 6, 3s 2, 3p 6, 4s 2, 3d 10, 4p 3 Let’s check our math. 18 + 2 + 10 + 3 = 33, the right number of electrons in a neutral arsenic atom, As. Since we followed the periodic table, we did not have to memorize the fact that the 4s orbital is filled before the 3d orbitals. The set of three 4p orbitals is only half-filled. ELECTRON CONFIGURATIONS

13. Section 8.4 Ions: Electron Configurations and Sizes Return to TOC 13 Because the elements N and P are directly above arsenic, As, in the periodic table, they also have half- filled p subshells. As a result, these three elements have many chemical similarities. Now we can begin to see why Mendeleev was able to predict the properties of elements and compounds that had not yet been discovered in 1869. ELECTRON CONFIGURATIONS

14. Section 8.4 Ions: Electron Configurations and Sizes Return to TOC Electron Orbital Configurations The configuration may be written by using boxes to represent each orbital All orbitals MUST be in increasing energy and MUST contain a label 1s 2s 2p 14 ELECTRON CONFIGURATIONS

15. Section 8.4 Ions: Electron Configurations and Sizes Return to TOC Electron Orbital Configurations 1s 2s 2p Arrows are used to represent each electron Before we begin….. 15 ELECTRON CONFIGURATIONS

16. Section 8.4 Ions: Electron Configurations and Sizes Return to TOC Three Rules Aufbau’s Principle – lower energy orbitals fill before proceeding to higher energy orbitals Hund’s Rule – When there are multiple orbitals available in a sublevel, one electron is placed in each orbital before doubling up the electrons Pauli’s Exclusion Principle – Within each orbital, e- must spin in opposite directions; each orbital in a sublevel must spin in the same direction. 16 ELECTRON CONFIGURATIONS

17. Section 8.4 Ions: Electron Configurations and Sizes Return to TOC Aufbau’s Principle To get the orbitals in increasing energy, just follow the periodic table like you would read a book. 1s2s2p3s3p4s3d4p5s4d5p6s4f5d6p 17 ELECTRON CONFIGURATIONS

18. Section 8.4 Ions: Electron Configurations and Sizes Return to TOC Hund’s Rule Never double up electrons in an orbital until each orbital in that sublevel has one electron. Once each orbital in a sublevel has one electron, then begin to double up the electrons. 18 ELECTRON CONFIGURATIONS

19. Section 8.4 Ions: Electron Configurations and Sizes Return to TOC Pauli’s Exclusions Principle Electrons will take the lowest energy configuration possible. This means: 1.All unpaired e- must spin in the same direction. 2.All paired e- must spin in opposite directions 19 ELECTRON CONFIGURATIONS

20. Section 8.4 Ions: Electron Configurations and Sizes Return to TOC Electron Orbital Configurations 1s 2s 2p Hydrogen Atomic # =1, 1e- 20 ELECTRON CONFIGURATIONS

21. Section 8.4 Ions: Electron Configurations and Sizes Return to TOC Electron Orbital Configurations 1s 2s 2p Helium – Atomic Number = 2 21 ELECTRON CONFIGURATIONS

22. Section 8.4 Ions: Electron Configurations and Sizes Return to TOC Electron Orbital Configurations 1s 2s 2p Boron – Atomic Number = 5 22 ELECTRON CONFIGURATIONS

23. Section 8.4 Ions: Electron Configurations and Sizes Return to TOC Stable Compounds Atoms in stable compounds usually have a noble gas electron configuration. 23 ELECTRON CONFIGURATIONS

24. Noble Gas Configuration What is a noble gas? Noble gases are located in group 8A, 18 on the periodic table. Noble gases are extremely unreactive, because their outer energy level is filled 24

25. Noble Gas Configurations Noble gases include: He Ne Ar Kr Xe Rn 25

26. Noble Gas Configurations Aufbau tells us that all lower sublevels MUST be filled before filling sublevels of higher energy. This results in us writing the same information repeatedly when making short hand configurations: Mn 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 5 Cl 1s 2 2s 2 2p 6 3s 2 3p 5 Ca 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 26

27. Noble Gas Configurations Rules: Choose the largest noble gas that has an atomic number LESS than the element you are working with. For Mn, the largest noble gas is Ar 27

28. Noble Gas Configurations Because we know that lower sublevels are already filled, we can substitute part of the configuration with a noble gas: Mn 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 5 Ar 1s 2 2s 2 2p 6 3s 2 3p 6 Therefore we write: [Ar] 4s 2 3d 5 28

29. Noble Gas Configurations Now try it for Cl Cl 1s 2 2s 2 2p 6 3s 2 3p 5 The largest noble gas is Ne 1s 2 2s 2 2p 6 [Ne] 3s 2 3p 5 Valence electrons – these ARE used in bonding Core electrons – these are NOT used when bonding 29

30. Noble Gas Configurations Write the noble gas configurations for: As I Pb Au W 30

31. Noble Gas Configurations Write the noble gas configurations for: As [Ar] 4s 2 3d 10 4p 3 I[Kr] 5s 2 4d 10 5p 5 Pb[Xe] 6s 2 4f 14 5d 10 6p 2 Au [Xe] 6s 2 4f 14 5d 9 W [Xe] 6s 2 4f 14 5d 4 31

32. Exceptional Configurations ….and ions 32

33. Exceptions to Aufbau There is a general stability associated with electron configurations Filled sublevels are MOST stable ½ Filled sublevels are stable All other configurations for sublevels are LEAST stable 33

34. Exceptions to Aufbau Sometimes by moving electrons between sublevels that are close in energy, atoms can achieve a more stable configuration. Examples include: s2d4s2d4 Because d 5 is ½ filled and more stable, the atom takes on the configuration of s1d5s1d5 34

35. Exceptions to Aufbau Cr [Ar] 4s 1 3d 5 Mo [Kr] 5s 1 4d 5 W [Xe] 6s 1 4f 14 5d 5 35

36. Exceptions to Aufbau Another exception occurs with the configuration: s2d9s2d9 Again, by moving 1e- from the “s” sublevel to the “d” sublevel, the “d” sublevel becomes filled. s 1 d 10 36

37. Exceptions to Aufbau Cu [Ar]4s 1 3d 10 Ag [Kr]5s 1 4d 10 Au [Xe]6s 1 4f 14 5d 10 37

38. WARNING Exceptional configurations only happen between “s” and “d” sublevels….NEVER between “s” and “p” sublevels. 38