1. Classification of the Elements
Section 6.2
Classification of the Elements

2. Objectives
Explain why elements in the same group have similar properties.
Identify the 4 blocks of the periodic table based on electron configuration.

3. What do these elements have in common?
The Periodic Table
Period 1 hydrogen 1s1
Period 2 lithium 1s22s1
Period 3 sodium 1s22s22p63s1
Period 4 potassium 1s22s22p63s23p64s1
What do these elements have in common?

4. Classification by valence electrons
Atoms of the same group have similar properties because they have the same number of valence electrons.
The number (in the group number) that accompanies the “A” designations tells you the number of valence electrons for that element.
There is one exception . . .

5. Classification by valence electrons
See p. 183 Fig. 7

6. Classification by energy level
The period number corresponds to the energy level of the valence electrons.
Valence electrons will always be in the highest energy level.
Where are the valence electrons for Ga?
How many valence electrons does Ga have?

7. Classification by “Block”
The Periodic Table can be viewed as arranged into blocks.
Each block corresponds to the sublevel in which the outermost electrons are located.

8. Classification by “block”

9. Classification by “Block”
s block: groups IA (electron configuration ends with s1) & IIA (electron configuration ends with s2 )
p block: groups IIIA to VIIIA (electron configurations ending with p1, p2, p3, p4, p5, & p6 respectively)
All p block elements have a filled s orbital
d block: transition metals
All d block elements have a filled s orbital BUT . . .

10. Energy level for d orbitals is n -1
(Remember n is the principal energy level or period number)
Example: Fe (atomic # 26) is [Ar] 4s2 3d6

11. Classification by “Block”
f block: Inner transition elements
s sublevel is filled
electron configurations end with n-2 f1-14
(Note: the energy level for f orbitals is n-2)
f sublevel does not “fill” with electrons in a predictable way

13. Practice Problems
Without using the periodic table, determine the group, period, and block of an atom of this configuration: [Kr] 5s2 4d10 5p5
Write the electron configuration for a group 2B element in period 4.
What elements have the following valence electron configuration: s2 p3?