1. Chapter 3 Atoms and Elements 3.7 Electron Energy Levels 1

2. Energy Levels Energy levels are assigned numbers n = 1, 2, 3, 4, and so on. increase in energy as the value of n increases. are like the rungs of a ladder with the lower energy levels nearer the nucleus. 2

3. Energy Levels Energy levels have a maximum number of electrons equal to 2n 2. Energy levelMaximum number of electrons n = 12(1) 2 = 2(1) = 2 n = 22(2) 2 = 2(4) = 8 n = 32(3) 2 = 2(9) = 18 3

4. Orbitals An orbital is a three-dimensional space around a nucleus, where an electron is most likely to be found. has a shape that represents electron density (not a path the electron follows). can hold up to 2 electrons. 4

5. Orbitals A p orbital has a two-lobed shape. is one of three p orbitals in each energy level from n = 2. 5 An s orbital has a spherical shape around the nucleus. is found in each energy level.

6. Orbitals 6

7. Electron Level Arrangement In the electron level arrangement for the first 18 elements electrons are placed in energy levels (1, 2, 3, etc.), beginning with the lowest energy level there is a maximum number in each energy level. Energy levelNumber of electrons 12 (up to He) 28 (up to Ne) 38 (up to Ar) 42 (up to Ca) 7

8. Examples Write the electron level arrangement for each: 1. N 2. Cl 3. K 8

9. Examples Identify the element with each electron level arrangement: 1. 2, 2 2. 2, 8, 3 3. 2, 7 9

10. Electron Configurations of Multielectron Atoms Electron Configuration: A description of which orbitals are occupied by electrons. Degenerate Orbitals: Orbitals that have the same energy level. For example, the three p orbitals in a given subshell. Ground-State Electron Configuration: The lowest-energy configuration. Aufbau Principle (“building up”): A guide for determining the filling order of orbitals.

11. Electron Configurations of Multielectron Atoms Rules of the aufbau principle: 1.Lower-energy orbitals fill before higher-energy orbitals. 2.An orbital can only hold two electrons, which must have opposite spins (Pauli exclusion principle). 3.If two or more degenerate orbitals are available, follow Hund’s rule. Hund’s Rule: If two or more orbitals with the same energy are available, one electron goes into each until all are half-full. The electrons in the half-filled orbitals all have the same spin.

13. Electron Configurations of Multielectron Atoms n = 1 s orbital (l = 0) 1 electron H: 1s11s1 Electron Configuration

14. Electron Configurations of Multielectron Atoms 1s21s2 n = 1 s orbital (l = 0) 2 electrons H: He: Electron Configuration 1s11s1

15. Electron Configurations of Multielectron Atoms n = 2 s orbital (l = 0) 1 electrons 1s 2 2s 1 H: Li: Lowest energy to highest energy He: Electron Configuration 1s21s2 1s11s1

16. Electron Configurations and the Periodic Table Give expected ground-state electron configurations for the following atoms, draw – orbital filling diagrams and determine the valence shell ◦ O (Z = 8) ◦ Ca (Z = 20) ◦ Sr (Z = 38) ◦ Sn (Z = 50)

17. Valence Electrons The valence electrons determine the chemical properties of the elements. are the electrons in the highest energy level. are related to the group number of the element. Example: Phosphorus has 5 valence electrons. 5 valence electrons P in Group 5A(15) 2, 8, 5 17

18. Groups and Valence Electrons All the elements in a group have the same number of valence electrons. Example: Elements in group 2A (2) have two (2) valence electrons. Be2, 2 Mg 2, 8, 2 Ca 2, 8, 8, 2 Sr 2, 8, 18, 8, 2 18

19. Periodic Table and Valence Electrons Representative Elements Group Numbers 1 2 3 4 5 6 7 8 H He 1 2 Li Be B C N O F Ne 2,1 2,2 2,3 2,4 2,5 2,6 2,7 2,8 Na Mg Al Si P S Cl Ar 2,8,1 2,8,2 2,8,3 2,8,4 2,8,5 2,8,6 2,8,7 2,8,8 19

20. Examples State the number of valence electrons for each. A. O 1) 42) 63) 8 B. Al 1) 132) 33) 1 C. Cl 1) 22) 53) 7 20

21. Examples State the number of valence electrons for each. A. calcium 1) 12) 23) 3 B. group 6A (16) 1) 22) 43) 6 C. tin 1) 22) 43) 14 21

22. Examples How many electrons are in energy level 3 of the following A.Sulfurb.Phosphorous

23. Examples Identify the elements that have the following electron level Energy level123 a. 210 b. 286 c. 287 23

24. Electron-Dot Symbols An electron-dot symbol shows the valence electrons around the symbol of the element. for Mg has 2 valence electrons as single dots on the sides of the symbol Mg... ·Mg · or Mg · or ·Mg or ·Mg · 24

25. Writing Electron-Dot Symbols Electron-dot symbols for groups 1A (1) to 4A (14) use single dots. · · Na · · Mg · · Al · · C · · groups 5A (15) to 7A (17) use pairs and single dots. · · · · · P · : O · · · 25

26. Groups and Electron-Dot Symbols In a group, all the electron-dot symbols have the same number of valence electrons (dots). Example: Atoms of elements in Group 2A (2) each have 2 valence electrons. · Be · · Mg · · Ca · · Sr · · Ba · 26

27. Examples. A. X is the electron-dot symbol for 1) Na2) K3) Al.. B.. X.. is the electron-dot symbol of 1) B2) N3) P 27

28. Examples What is the dot Lewis structure of ◦ Carbon ◦ Magnesium ◦ Aluminum ◦ Argon

29. Atomic Size 29 Atomic size is described using the atomic radius; the distance from the nucleus to the valence electrons.

30. Atomic Radius Within A Group Atomic radius increases going down each group of representative elements. 30

31. Atomic Radius Across a Period Going across a period from left to right, an increase in the number of protons increases attraction for valence electrons. atomic radius decreases. 31

32. Examples Select the element in each pair with the larger atomic radius. A. Li or K B. K or Br C. P or Cl 32

33. Ionization Energy Ionization energy is the energy it takes to remove a valence electron. Na(g) + Energy (ionization) -> Na + (g) + e - 33

34. Ionization Energy In a Group Going up a group of representative elements, the distance decreases between nucleus and valence electrons. the ionization energy increases. 34

35. Ionization Energy Metals have lower ionization energies. Nonmetals have higher ionization energies. 35

36. Examples Select the element in each pair with the higher ionization energy. A. Li or K B. K or Br C. P or Cl 36