1. 1 Chapter 3 Atoms and Elements 3.7 Electron Energy Levels Copyright © 2009 by Pearson Education, Inc.

2. 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.

3. 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

4. 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.

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

6. 6 Orbitals

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

9. Solution Write the electron level arrangement for each: 1. N2, 5 2. Cl2, 8, 7 3. K2, 8, 8, 1 9

10. Learning Check Identify the element with each electron level arrangement: 1. 2, 2 2. 2, 8, 3 3. 2, 7 10

11. Solution Identify the element with each electron level arrangement: 1. Be2, 2 2. Al 2, 8, 3 3. F 2, 7 11