106 / 123
Organizing the Elements by Electron
Configuration
As you learned previously, electron configuration determines the chemical properties
of an element. Writing out electron configurations using the aufbau diagram can be
tedious. Fortunately, you can determine an atom’s electron configuration and its num-
ber of valence (outermost) electrons from its position on the periodic table. The
repeating patterns of the table reflect patterns of outer electron states. The electron
configurations for some of the group 1 elements are listed in
Table 3
. All four
configurations have a single electron in their outermost orbitals.
Valence electrons
Recall that electrons in the highest principal energy level of an atom are called valence
electrons. Each of the group 1 elements has one valence electron. The group 1 elements
have similar chemical properties because they have the same number of valence elec-
trons. This is one of the most important relationships in chemistry: atoms in the same
group have similar chemical properties because they have the same number of valence
electrons. Each group 1 element has a valence electron configuration of s
1
. Each group 2
element has a valence electron configuration of s
2
. Groups 1, 2, and 13 to 18 all have
their own valence electron configurations.
Table 3
Electron Configuration for the Group 1 Elements
Period 1
hydrogen
1s
1
1s
1
Period 2
lithium
1s2s
1
[He]2s
1
Period 3
sodium
1s
2
2s
2
2p
6
3s
1
[Ne]3s
1
Period 4
potassium
1s
2
2s
2
2p
6
3s
2
3p64s
1
[Ar]4s
1
FOCUS QUESTION
Why do elements in the same group have similar
properties?
LESSON 2
CLASSIFICATION OF THE ELEMENTS
Disciplinary Core Ideas
Crosscutting Concepts
Science & Engineering Practices
3D THINKING
C
C
C
S
E
P
D
C
I
COLLECT EVIDENCE
Use your Science Journal to
record the evidence you collect as
you complete the readings and
activities in this lesson.
INVESTIGATE
GO ONLINE
to find these activities and more resources.
Identify Crosscutting Concepts
Create a table of the
crosscutting concepts
and fill in examples you find as you read.
Revisit the Encounter the Phenomenon Question
What information from this lesson can help you answer the module question?
146
Module 5 • The Periodic Table and Periodic Law