1. Basic Chemistry Chapter 5 Electronic Structure and Periodic Trends
Chapter 5 Lecture
Basic Chemistry
Fifth Edition
Chapter 5 Electronic Structure and Periodic Trends
5.6 Trends in Periodic Properties
Learning Goal Use the electron configurations of elements to explain the trends in periodic properties.

2. Valence Electrons
The valence electrons, the s and p sublevels in the highest energy level,
are related to the group number of the element.
determine the chemical properties of an element.
Example: Phosphorus has five valence electrons.
P Group 5A (15) s2 2s2 2p6 3s2 3p3

3. Group Numbers and Valence Electrons
All the elements in a group have the same number of valence electrons. Elements in Group 2A (2) have two (2) valence electrons. Be 1s2 2s2 Mg 1s2 2s2 2p6 3s2 Ca 1s2 2s2 2p6 3s2 3p6 4s2 Sr 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2

4. Periodic Table and Valence Electrons

5. Learning Check
Select the correct number of valence electrons for each.
O (1) 4 (2) 6 (3) 8
Al (1) 13 (2) 3 (3) 1
Cl (1) 2 (2) 5 (3) 7
Group 6A (16) (1) 2 (2) 4 (3) 6
Tin (1) 2 (2) 4 (3) 14

6. Solution Select the correct number of valence electrons for each.
Cl (3) 7
Group 6A (16) (3) 6
Tin (2) 4

7. Learning Check State the number of valence electrons for each.
1s2 2s2 2p6 3s2 3p3
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p4
1s2 2s2 2p5

8. Solution State the number of valence electrons for each.
1s2 2s2 2p6 3s2 3p3 5 valence electrons
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p4
6 valence electrons
1s2 2s2 2p5 7 valence electrons

9. Electron-Dot Symbols An electron-dot symbol
indicates the number of valence electrons as dots around the symbol of the element.
for Mg shows two valence electrons placed as single dots on the sides of the symbol Mg.
Mg 1s2 2s2 2p6 3s2
Any of the following would be an acceptable Lewis symbol for magnesium, which has two valence electrons:

10. Electron-Dot Symbols

11. Atomic Size
Atomic size is determined by the distance of the valence electrons from the nucleus.

12. Atomic Size The atomic radius increases
going down each group of representative elements.
as the number of energy levels increases.

13. Atomic Size
The atomic radius decreases
going from left to right across a period.
as more protons increase the nuclear attraction for valence electrons.

14. Learning Check
Select the element in each pair with the larger
atomic radius.
Li or K
K or Br
P or Cl

15. Solution
Select the element in each pair with the larger
atomic radius.
A. K is larger than Li.
B. K is larger than Br.
C. P is larger than Cl.

16. Ionization Energy
Ionization energy is the energy it takes to remove a valence electron.

17. Ionization Energy Metals have 1–3 valence electrons.
lower ionization energies.
Nonmetals have
5–7 valence electrons.
higher ionization energies.
Noble gases have
complete octets (He has two valence electrons).
the highest ionization energies in a period.

18. Learning Check
Select the element in each pair with the higher
ionization energy.
A. Li or K
B. K or Br
C. P or Cl

19. Solution
Select the element in each pair with the higher
ionization energy.
A. Li has a higher ionization energy than K.
B. Br has a higher ionization energy than K.
C. Cl has a higher ionization energy than P.

20. Metallic Character
Elements with high metallic character lose their electrons easily. Elements that are
metals lose their electrons easily.
metalloids lose electrons, but not as easily as metals.
nonmetals do not easily lose their electrons.

21. Summary of Periodic Table Trends

22. Concept Map