1 Chapter 3 Electronic Structure and Periodic Law 3.6 Property Trends within the Periodic Table Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

2 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

3 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 · · ·

4 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 ·

5 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

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

7 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

8 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

9 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

10 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

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

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

13 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

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

15 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

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