1. Electron Configurations,
Orbital Diagrams,
Electron Configurations,
&
Valence Electrons

3. Bohr’s Model: electrons would exist in different rings around the nucleus just like the planets are in different orbits around the sun. This is sometimes called the planetary model of the atom

4. 7 orbits correspond to 7 periods on Periodic Table.
Bohr’s Atom
7 orbits correspond to 7 periods on Periodic Table.

5. Which Orbit has the lowest energy?
n = 1, the orbit closest to the nucleus.

6. Bohr’s model was replaced by the quantum mechanical model of the atom.

7. This new model uses principle quantum levels that are similar to Bohr’s orbits, but are then divided into sublevels

8. The principle quantum level is a number from 1-7, with 1 being the lowest energy and 7 being the highest in energy.
The sublevels are s, p, d, and f

9. These numbers and letters correspond to the periods and the “blocks” on the periodic table.

10. Each sublevel has a least one orbital.
Each orbital can hold 2 electrons

11. The s sublevel only has 1 orbital, and each orbital holds 2 electrons
Which matches the 2 elements in each period of the s block
Shape: Sphere

12. The p sublevel has 3 orbitals, and each orbital holds 2 electrons, for a total of 6 electrons – Matching the 6 elements in each period of the p block
Shape: dumbbell or peanut

13. The d sublevel has 5 orbitals, and each orbital holds 2 electrons, for a total of 10 electrons – matching the 10 elements in each period of the d block
Shape: clover/
double dumbbell

14. The f sublevel has 7 orbitals, and each orbital holds 2 electrons, for a total of 14 electrons – matching the 14 elements
Funky / flower

15. We put together the principle quantum number and sublevel letter to talk about a specific orbital
But not all sublevels are possible for each energy level.

16. 1 s 2 s, p 3 s, p, d 4 – 7 s, p, d, f 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f
Principle Quantum Level Possible Sublevels
1 s
2 s, p
3 s, p, d
4 – 7 s, p, d, f 1s
2s 2p
3s 3p 3d
4s 4p 4d 4f
5s 5p 5d 5f
6s 6p 6d (6f)
7s 7p (7d 7f)

17. The arrangement of electrons in an atom is called an orbital diagram or electron configuration.

18. 1) There are three rules that we must follow when making an orbital diagram (OD) or an electron configuration (EC):

19. A) The aufbau principle says electrons must fill lower energy levels before electrons can fill higher energy levels.
This means 1s is filled before 2s, etc

20. B) The Pauli exclusion principle says that only two electrons can fill each orbital…and they must have opposite spins.
No Yes

21. C) Hund’s rule says electrons must spread out in the orbitals of each sublevel (p, d, or f) before they double up.
Yes No
□ □ □ □ □ □
2p 2p

22. 2) If we use boxes to represent orbitals, then the following aufbau diagram shows all the possible places an electron could be:

23. Remember: s has 1 orbital…..holds 2 electrons
p has …..holds 6 electrons
d has 5 …..holds 10 electrons
f has 7 …..holds 14 electrons

24. Notice that the energy increases from bottom to top,
High
Energy
Low
Energy

25. and some of the orbitals do not fill in the same number order as the others.

26. Fill from the bottom to the top, spreading out the electrons before doubling them up

28. □ □ □ □ 1s 2s 3s 2p 3p
Hydrogen H

29. □ □ □ □ 1s 2s 3s 2p 3p
Helium He
Completely
Filled

30. □ □ □ □ 1s 2s 3s 2p 3p
Lithium Li

31. □ □ □ □ 1s 2s 3s 2p 3p
Beryllium Be

32. □ □ □ □ 1s 2s 3s 2p 3p
Boron B

33. □ □ □ □ 1s 2s 3s 2p 3p
Carbon C

34. □ □ □ □ 1s 2s 3s 2p 3p
Nitrogen N

35. □ □ □ □ 1s 2s 3s 2p 3p
Oxygen O

36. □ □ □ □ 1s 2s 3s 2p 3p
Fluorine F

37. □ □ □ □ 1s 2s 3s 2p 3p
Neon Ne
Completely
Filled

38. □ □ □ □ 1s 2s 3s 2p 3p
Sodium Na

39. □ □ □ □ 1s 2s 3s 2p 3p
Magnesium Mg

40. □ □ □ □ 1s 2s 3s 2p 3p
Aluminum Al

41. □ □ □ □ 1s 2s 3s 2p 3p
Silicon Si

42. □ □ □ □ 1s 2s 3s 2p 3p
Phosphorus P

43. □ □ □ □ 1s 2s 3s 2p 3p
Sulfur S

44. □ □ □ □ 1s 2s 3s 2p 3p
Chlorine Cl

45. □ □ □ □ 1s 2s 3s 2p 3p
Argon Ar
Completely
Filled

46. 3) The correct order of filling is: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p
Notice: s block fills in period 1
p block fills in period 2
d block fills in period 3: which is 1 behind the actual period
f block fills in period 4: which is 2 behind the actual period

47. n = period #
s & p block fill at n
d block fills at n – 1
f block fills at n - 2

48. 4) Orbital Diagram: Orbitals are sometimes shown as boxes in a horizontal row
Remember: s = 1 orbital
p = 3 orbitals
d = 5 orbitals
f = 7 orbitals

49. 5) Arrows are used to represent the electrons, so if two arrows go in the same box, one points up and the other points down.

50. □ □ □ □
Nitrogen N
7 electrons 2p 2s 1s
Becomes:
□ □ □ □ □
1s 2s p

51. □ □ □□□ □ □□□ □ □□□□□ Cobalt (27 electrons – 27 arrows)
1s 2s 2p 3s 3p 4s 3d

52. Cations and anions
* Ions: work the same way but remember that electrons are negative. +2 means you lost two electrons, -2 means you gained two electrons.

53. Try Bromine

54. □ □ □□□ □ □□□ □ □□□□□ □□□ Bromine (35 electrons)
□ □ □□□ □ □□□ □ □□□□□ □□□
1s 2s 2p 3s 3p 4s 3d 4p

55. Try Oxygen, O2- and Gallium on the back of your notes

56. Oxygen
□ □ □□□ □ □□□ □ □□□□□ □□□
1s 2s 2p 3s 3p 4s 3d p

57. O-2
□ □ □□□ □ □□□ □ □□□□□ □□□
1s 2s 2p 3s 3p 4s 3d p

58. Gallium
□ □ □□□ □ □□□ □ □□□□□ □□□
1s 2s 2p 3s 3p 4s 3d p

59. 6) Electron Configuration: Instead of drawing boxes and arrows, the number of electrons in each sublevel is turned into a superscript and is written with the quantum number and the sublevel letter.

60. A) If all the orbitals are filled, the entire sequence would be:
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f14 6d10 7p6

61. Nitrogen N
□ □ □ □ □
1s 2s p
Becomes:
1s2 2s2 2p3

62. □ □ □□□ □ □□□ □ □□□□□ Cobalt 1s 2s 2p 3s 3p 4s 3d Becomes:

63. Try Bromine, Oxygen, O2-, Ca 2+ and Gallium on the back of your notes

64. □ □ □□□ □ □□□ □ □□□□□ □□□ Bromine (35 electrons)
□ □ □□□ □ □□□ □ □□□□□ □□□
1s 2s 2p 3s 3p 4s 3d 4p
Becomes:
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5

65. Electron configurations for:
Oxygen: 1s22s22p4
O2- : 1s22s22p6
Ca2+ : 1s22s22p63s23p6
Gallium: 1s22s22p63s23p64s23d104p1

66. 7) Short cut: Noble gas configuration
7) Short cut: Noble gas configuration. Instead of writing out the entire electron configuration, we can use the previous noble gas to take the place of part of the electron configuration: must start with a noble gas

67. Example:
Magnesium: 1s22s22p63s2
Neon: 1s22s22p6
Noble Gas configuration:
Magnesium: [Ne] 3s2

68. Example: Polonium: Xenon: Polonium: [Xe] 6s24f145d106p4
1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p4
Xenon:
1s22s22p63s23p64s23d104p65s24d105p6
Polonium: [Xe] 6s24f145d106p4

69. Try Bromine, Oxygen, O2-, Ca 2+ and Gallium on the back of your notes

70. Noble gas configurations
Bromine [Ar] 4s2 3d10 4p5 Oxygen: [He] 2s22p4 O2-: [He] 2s22p6 Ca2+ : [Ne] 3s23p6 Gallium: [Ar] 4s23d104p1

71. Valence Electrons: Electrons in the outer-most orbital – which is the highest energy level.
Very important: electrons involved in chemical bonds – determine chemical properties of element

72. These electrons are called valence electrons.

73. Only the s and p block electrons are counted…so the number of valence electrons must be a number from 1 to 8

74. Electron Dot Diagrams (Lewis Dot Diagrams):
The number of valence electrons makes a big difference in how the element will bond, so to make it easy to predict, we draw electron dot diagrams.

75. A) In an electron dot diagram, we use the symbol of the element and dots to represent the number of valence electrons. The number of dots matches the group number on the Periodic Table.

76. B) Only s and p electrons with the highest quantum number count for dot diagrams, even if there are d and f electrons

77. Lithium = 1s22s1
So Li

78. Beryllium = 1s2 2s2
So Be

79. Boron = 1s2 2s22p1
So B

80. Carbon = [He] 2s22p2
So C

81. Nitrogen = [He] 2s22p3
So N

82. Oxygen = 1s2 2s22p4
So O

83. Fluorine = 1s2 2s22p5
So F

84. Neon = 1s22s22p6 or [Ne] So Ne All noble gases have full outer shells:
8 valence electrons (except He which is full at 2, since it only has the s orbital)

85. Magnesium = 1s22s22p63s2 So

86. Magnesium = 1s22s22p63s2 So Mg

87. Polonium: 1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p4

88. Polonium: 1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p4 So Po

89. Look at your Periodic Table - Notice:
The A group number = the number of valence electrons (except for He)
Look at your Periodic Table Notice: the A group number = the number of valence electrons 1A 8A 2A 7A 3A 4A 5A 6A