1. Chapter 2 Atoms and Elements
Electron Energy Levels

2. Electromagnetic Radiation
Consists of energy particles called photons that travel as waves.
Includes low energy particles that have long wavelengths and high energy particles that have short wavelengths.

3. Electromagnetic Spectrum

4. Electron Energy Levels
Electrons are arranged in specific energy levels called shells.
The first energy level (n=1) contains electrons that have the lowest energy.
The energy levels are labeled 1, 2, 3, and so on.

5. Number of Electrons
Electrons of similar energy are grouped in energy levels.
The maximum number of electrons in any energy level is equal to 2n2. n = 1 2(1)2 = n = 2 2(2)2 = 8 n = 3 2(3)2 = 18 n = 4 2(4)2 = 32

7. Learning Check A. The correct electron shell arrangement for
nitrogen is
1) 7 2) 2, 5 3) 2, 2, 3
B. The correct electron shell arrangement for
sulfur is
1) 2,6 2) 8,2,6 3) 2, 8, 6
C. The element in period 3 with two electrons
in the outermost energy level is
1) Mg 2) Ca 3) Be

8. Solution A. The correct electron shell arrangement for nitrogen is
2) 2, 5
B. The electron configuration for sulfur is
3) 2, 8, 6
C. The element in period 3 with two electrons
in the outermost energy level is
1) Mg

9. Learning Check
Indicate the number of electrons in the last electron shell for each of the following elements:
A. O 1) ) 6 3) 8
B. Al 1) ) 3 3) 1
C. Cl 1) 2 2) 5 3) 7

10. Solution
Indicate the number of electrons in the last electron shell for each of the following elements:
A. O 2) 6
B. Al 2) 3
C. Cl 3) 7

11. Periodic Law
All the elements in a group have the same number of electrons in their outermost shells (valence electrons).
Elements in a group have similar chemical and physical properties.
Example: Group 2
Be 2, 2
Mg 2, 8, 2
Ca 2, 8, 8, 2

12. Learning Check
Specify if each pair has chemical properties that are similar or not similar:
A. Cl and Br
B and
C and
D. P and S
E. O and S

13. Solution
Specify if each pair has chemical properties that are 1) similar or 2) not similar:
A. Cl and Br similar
B and not similar
C and similar
D. P and S not similar
E. O and S similar

14. Energy Level Changes Electrons are in discrete energy levels.
An electron absorbs energy to “jump” to a higher energy level.
When an electron falls to a lower energy level, energy is emitted.
In the visible range, the emitted energy appears as a color.

15. Learning Check Answer with 1) Energy absorbed
2) Energy emitted 3) No change in energy
A.What energy change takes place when an electron in a hydrogen atom moves from the first (n=1) to the second shell (n=2)?
B.What energy change takes place when an electron moves from the third shell (n=3) to the second shell (n=2)?

16. Solution
A.What energy change takes place when an electron in a hydrogen atom moves from the first (n=1) to the second shell (n=2)?
Energy absorbed
B.What energy change takes place when an electron moves from the third shell to the second shell?
Energy emitted

17. Chapter 2 Atoms and Elements
2.7 Subshells and Orbitals

18. Subshells
Within each energy level, electrons are grouped into energy sublevels or subshells.
All electrons in a subshell have the same energy.
The different subshells are designated by the letters s, p, d, f.

19. Number of Subshells in a Shell
The number of subshells in each shell is the same as the shell number. Shell Number of Types of Number Subshells Subshells n= s, 4p, 4d, 4f n= s, 3p, 3d n= s, 2p n= s

20. Energy Levels of Subshells
The s subshell has the lowest energy in any shell followed by the p, d, and f subshells. 3d n = 3 3p 3s 2p 2s n = 1 1s
n = 2

21. Orbitals
An orbital is a 3 dimensional space around a nucleus in which an electron is most likely to be found.
The shape represents electron density (not a path the electron follows).**
Each orbital can hold up to 2 electrons.

22. Subshells and Orbitals
Each subshell has a specific number of orbitals.
Each s subshell contains one s orbital.
Each p subshell contains three p orbitals.
Each d subshell contains five d orbitals.
Each f subshell contains seven f orbitals.

23. s and p Orbitals
In an atom, all the orbitals are centered around the nucleus. For example, the illustration of the combination of s and p orbitals is

24. Electrons in Each Subshell

25. Learning Check A. How many electrons can occupy a p orbital?
1) 1 2) 2 3) 3
B. How many p orbitals are in the 2p subshell?
C. How many d orbitals are in the 4d subshell?
1) 1 2) 3 3) 5
D. What is the maximum number of electrons
in the 3d subshell?
1) 2 2) 5 3) 10

26. Solution A. How many electrons can occupy a p orbital? 2) 2
B. How many p orbitals are in the 2p subshell?
3) 3
C. How many d orbitals are in the 4d subshell?
3) 5
D. What is the maximum number of electrons
in the 3d subshell?
3) 10

27. Chapter 2 Atoms and Elements
2.8 Electron Configurations

28. Electron Configuration
An electron configuration
Is a list of the subshells and the number of electrons in each in order of increasing energy.
Contains superscripts that give the number of electrons in each subshell.
Of neon is as follows: number of electrons in each subshell 1s2 2s2 2p6

29. Subshell Location on the Periodic Table
The periodic table contains subshell blocks arranged in order of increasing energy.

30. Subshell Blocks
There is a specific number of electrons in each subshell block.
1 s1 s p1 p2 p3 p4 p5 p6 2
d1 - d10 4 5 6
f1 - f14

31. Writing an Electron Configuration
An electron configuration is written by:
Locating the element on the periodic table.
Starting with H and writing each subshell notation and electrons in order.

32. Some Electron Configurations
First Period
H 1s1
He 1s2
Second Period
Li s2 2s1
C 1s2 2s2 2p2
Third Period
Na 1s2 2s2 2p6 3s1
Al 1s2 2s2 2p6 3s2 3p1
S 1s2 2s2 2p6 3s2 3p4

33. Electron Configurations for Atomic Numbers 1-18

34. Electron Configurations for Elements 19-36

35. Noble Gas Notation
A noble gas notation is used to abbreviate the completed subshells as [noble gas].
For example, the complete configuration of bromine is
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5
Ar configuration
The noble gas notation for bromine is
[Ar] 4s2 3d10 4p5

36. Learning Check
Using the periodic table, write the complete electronic configuration and noble gas notation for each of the following elements:
A. Cl
B. Sr
C. I

37. Solution A. Cl 1s2 2s2 2p6 3s2 3p5 [Ne] 3s23p5 B. Sr
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2
[Kr] 5s2
C. I
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p5
[Kr] 5s2 4d10 5p5

38. Group Numbers and Subshells
The Group Number is the sum of the s and p electrons in the outermost shell (valence electrons).