1. Trends in Periodic Table Properties
General, Organic, and Biological Chemistry
Fourth Edition
Karen Timberlake
Chapter 3
Atoms and Elements
3.8
Trends in Periodic Table Properties
Lectures
© 2013 Pearson Education, Inc.

2. Valence Electrons The valence electrons
determine the chemical properties of the elements.
are the electrons in the outermost, highest energy level.
are related to the group number of the element.
Example: Phosphorus has 5 valence electrons.
5 valence
electrons
P Group 5A(15) 1s22s22p63s23p3

3. Groups and Valence Electrons
All the elements in a group have the same number of valence electrons. Example: Elements in Group 2A (2) have two (2) valence electrons. Be 1s22s2 Mg 1s22s22p63s2 Ca [Ar]4s2 Sr [Kr]5s2

4. Periodic Table and Valence Electrons

5. Learning Check
Identify the number of valence electrons for each of the following: 1. O A. 4 B. 6 C Al A. 13 B. 3 C Cl A. 2 B. 5 C. 7

6. Solution
Identify the number of valence electrons for each of the following: 1. O B Al B Cl C. 7

7. Learning Check
Identify the number of valence electrons for each of the following: 1. Calcium A. 1 B. 2 C Group 6A (16) A. 2 B. 4 C Tin A. 2 B. 4 C. 14

8. Solution
Identify the number of valence electrons for each of the following: 1. Calcium B Group 6A (16) C Tin B. 4

9. Learning Check
Identify the number of valence electrons for each of the following: 1. 1s22s22p63s23p1 2. 1s22s22p63s2 3. 1s22s22p5

10. Solution Identify the number of valence electrons for each of the
following:
1. 1s22s22p63s23p1 3
2. 1s22s22p63s2 2
3. 1s22s22p5 7

11. Electron-Dot Symbols An electron-dot symbol
indicates valence electrons
as dots around the symbol of the element.
of Mg shows two valence electrons as single dots on the sides of the symbol Mg.

12. Writing Electron-Dot Symbols
The electron-dot symbols for
Groups 1A (1) to 4A (14) use single dots:
Groups 5A (15) to 7A (17) use pairs and single dots:

13. Groups and Electron-Dot Symbols
In a group, all the electron-dot symbols have the same number of valence electrons (dots). Example: Atoms of elements in Group 2A (2) each have 2 valence electrons. Group 2A (2) · Be · · Mg · · Ca · · Sr · · Ba ·

14. Learning Check
 1. X is the electron-dot symbol for A. Na B. K C. Al   2.  X  is the electron-dot symbol for
A. B B. N C. P

15. Solution  1. X is the electron-dot symbol for both A. Na B. K  
B. N C. P

16. Atomic Size Atomic size is described using the atomic radius.
is the distance from the nucleus to the valence electrons.
increases going down a group.
decreases going across a period from left to right.

17. Atomic Radius

18. Learning Check
Select the element in each pair with the larger atomic radius. 1. Li or K 2. K or Br 3. P or Cl

19. Solution
Select the element in each pair with the larger atomic radius. 1. K is larger than Li. 2. K is larger than Br. 3. P is larger than Cl.

20. Ionization Energy Ionization energy
is the energy it takes to remove a valence electron from an atom in the gaseous state.
Na(g) + Energy (ionization) Na+(g) + e–
decreases down a group, increasing across the periodic table from left to right.

21. Ionization Energy and Valence Electrons

22. Ionization Energy The ionization energies of metals are low.
nonmetals are high.

23. Metallic Character
The metallic character increases when an element can
lose its valence electrons more easily, it
increases down a group where electrons are easier to remove.
decreases across the period because electrons are harder to remove.

24. Metallic Character

25. Periodic Table Trend Summary

26. Learning Check
Select the element in each pair with the higher ionization energy. 1. Li or K 2. K or Br 3. P or Cl

27. Solution
Select the element in each pair with the higher ionization energy. 1. Li is higher than K. 2. Br is higher than K. 3. Cl is higher than P.