1. 1 Chapter 3 Atoms and Elements 3.8 Periodic Trends Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

2. 2 Valence Electrons The valence electrons determine the chemical properties of the elements. are the electrons in the 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) 2, 8, 5

3. 3 All the elements in a group have the same number of valence electrons. Example: Elements in group 2A(2) have two (2) valence electrons. Be2, 2 Mg 2, 8, 2 Ca 2, 8, 8, 2 Sr 2, 8, 18, 8, 2 Groups and Valence Electrons

4. 4 Periodic Table and Valence Electrons Representative Elements Group Numbers 1 2 3 4 5 6 7 8 H He 1 2 Li Be Al C N O F Ne 2,1 2,2 2,3 2,4 2,5 2,6 2,7 2,8 Li Mg Ge Si P S Cl Ar 2,8,1 2,8,2 2,8,3 2,8,4 2,8,5 2,8,6 2,8,7 2,8,8

5. 5 State the number of valence electrons for each. A. O 1) 42) 63) 8 B. Al 1) 132) 33) 1 C. Cl 1) 22) 53) 7 Learning Check

6. 6 State the number of valence electrons for each. A. O 2) 6 B. Al 2) 3 C. Cl 3) 7 Solution

7. 7 State the number of valence electrons for each. A. calcium 1) 12) 23) 3 B. group 6A (16) 1) 22) 43) 6 C. tin 1) 22) 43) 14 Learning Check

8. 8 State the number of valence electrons for each. A. calcium 2) 2 B. group 6A (16) 3) 6 C. tin 2) 4 Solution

9. 9 State the number of valence electrons for each. A. 2, 8, 5 B. 2, 8, 8, 2 C. 2, 7 Learning Check

10. 10 State the number of valence electrons for each. A. 2, 8, 55 B. 2, 8, 8, 22 C. 2, 77 Solution

11. 11 Electron-Dot Symbols An electron-dot symbol shows the valence electrons around the symbol of the element. for Mg has two valence electrons as single dots on the sides of the symbol Mg... ·Mg · or Mg · or ·Mg or ·Mg · Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

12. 12 Writing Electron-Dot Symbols Electron-dot symbols for groups 1A(1) to 4A(14) use single dots. · · Na · · Mg · · Al · · C · · groups 5A(15) to 7A(17) use pairs and single dots. · · · · · · · P · : O · : Cl : · · · :

13. 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. · Be · · Mg · · Ca · · Sr · · Ba ·

14. 14 A. X is the electron-dot symbol for 1) Na2) K3) Al B. X is the electron-dot symbol of 1) B2) N3) P Learning Check

15. 15 A. X is the electron-dot symbol for 1) Na2) K B. X is the electron-dot symbol of 2) N3) P Solution

16. 16 Atomic Size Atomic size is described using the atomic radius; the distance from the nucleus to the valence electrons. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

17. 17 Atomic Radius Within A Group Atomic radius increases going down each group of representative elements. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

18. 18 Atomic Radius Across a Period Going across a period left to right, an increase in number of protons increases attraction for valence electrons. atomic radius decreases. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

19. 19 Learning Check Select the element in each pair with the larger atomic radius. A. Li or K B. K or Br C. P or Cl

20. 20 Solution Select the element in each pair with the larger atomic radius. A. K B. K C. P

21. 21 Ionization Energy Ionization energy is the energy it takes to remove a valence electron. Na(g) + Energy (ionization)  Na + (g) + e -

22. 22 Ionization Energy In a Group Going up a group of representative elements, the distance decreases between nucleus and valence electrons. the ionization energy increases. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

23. 23 Ionization Energy Metals have lower ionization energies. Nonmetals have higher ionization energies. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

24. 24 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

25. 25 Solution Select the element in each pair with the higher ionization energy. A. Li B. Br C. Cl