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Chapter 9 Electron Configuration and Periodic Trends 9.6 Periodic Trends of the Elements 1 Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings Valence Electrons The valence electrons • Determine the chemical properties of the elements. • Are the electrons in the s and p sublevels 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 1s22s22p6 3s23p3 Group Number 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 1s2 2s2 Mg 1s2 2s2 2p6 3s2 Ca 1s2 2s2 2p6 3s2 3p6 4s2 Sr 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 3 Periodic Table and Valence Electrons Table 9.3 Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings 4 Learning Check State the number of valence electrons for each: A. O 1) 4 2) 6 3) 8 5 B. Al 1) 13 2) 3 3) 1 C. Cl 1) 2 2) 5 3) 7 Solution State the number of valence electrons for each. A. O 2) 6 B. Al 2) 3 C. Cl 3) 7 6 Learning Check State the number of valence electrons for each. A. Calcium 1) 1 2) 2 3) 3 B. Group 6A (16) 1) 2 2) 4 3) 6 C. Tin 1) 2 2) 4 3) 14 7 Solution State the number of valence electrons for each. A. Calcium 2) 2 B. Group 6A (16) 3) 6 C. Tin 2) 4 8 Learning Check State the number of valence electrons for each. A. 1s2 2s2 2p6 3s2 3p3 B. 1s2 2s2 2p6 3s2 3p64s2 3d104p4 C. 1s22s22p5 9 Solution State the number of valence electrons for each. A. 1s2 2s2 2p6 3s2 3p3 5 B. 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p4 6 C. 1s22s22p5 7 10 Atomic Size Atomic radius •Is the distance from the nucleus to the valence electrons. 11 Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings Atomic Radius Within A Group Atomic radius increases • Going down each group of representative elements. • As the number of energy levels increases. 12 Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings Atomic Radius Across a Period Atomic radius decreases • Going from left to right across a period. • As more protons increase nuclear attraction for valence electrons. Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings 13 Learning Check Select the element in each pair with the larger atomic radius. A. B. C. 14 Li or K K or Br P or Cl Solution Select the element in each pair with the larger atomic radius. A. K B. K C. P 15 Sizes of Metal Atoms and Ions A positive ion • Has lost its valence electrons. • Is smaller (about half the size) than its corresponding metal atom. Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings 16 Size of Sodium Ion The sodium ion Na+ • Forms when the Na atom loses one electron from the 3rd energy level. • Is smaller than a Na atom. Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings 17 Sizes of Nonmetal Atoms and Ions A negative ion • Has a complete octet. • Increases the number of valence electrons. • Is larger (about twice the size) than its corresponding metal atom. Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings 18 Size of Fluoride Ion The fluoride ion F• Forms when a valence electron is added. • Has increased repulsions due to the added valence electron. • Is larger than F atom 19 Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings Learning Check 1. Which is larger in each of the following? A. K or K+ B. Al or Al3+ C. S2- or S 2. Which is smaller in each of the following? A. N3- or N B. Cl or ClC. Sr2+ or Sr 20 Solution 1. Which is larger in each of the following? A. K > K+ B. Al > Al3+ C. S2- > S 2. Which is smaller in each of the following? A. N < N3B. Cl < ClC. Sr2+< Sr 21 Ionization Energy Ionization energy • Is the energy it takes to remove a valence electron. Na(g) + Energy of Ionization Na+(g) + e- + Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings 22 Ionization Energy Metals have • 1-3 valence electrons. • Lower ionization energies. 23 Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings Ionization Energy Nonmetals have • 5-7 valence electrons. • Have higher ionization energies. 24 Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings Ionization Energy Nobel gases have • Complete octets (He has two valence electrons.) • Have the highest ionization energies in each period. 25 Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings Learning Check Select the element in each pair with the higher Ionization energy. A. B. C. 26 Li or K K or Br P or Cl Solution Select the element in each pair with the higher Ionization energy. A. B. C. 27 Li Br Cl