Chapter 5 Lecture 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. Fifth Edition Valence Electrons The valence determine the chemical properties of an element are the 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 2 5 valence P Group 5A(15) 1s 2 2s 2 2p 6 3s 2 3p 3 Group Number and Valence Electrons All the elements in a group have the same number of valence. Periodic Table and Valence Electrons Example: Elements in Group 2A (2) have two (2) valence. Be 1s 2 2s 2 Mg 1s 2 2s 2 2p 6 3s 2 Ca 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 Sr 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 3 4 State the number of valence for each: A. O B. Al C. Cl 1) 4 2) 6 3) 8 1) 13 2) 3 3) 1 1) 2 2) 5 3) 7 State the number of valence 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 5 6 1
State the number of valence for each. A. 1s 2 2s 2 2p 6 3s 2 3p 3 B. 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 4 C. 1s 2 2s 2 2p 5 Electron-Dot Symbols An electron-dot symbol indicates the valence as dots around the symbol of the element for Mg shows two valence placed as single dots on the sides of the symbol Mg.. Mg or Mg or Mg or Mg 7 8 Writing Electron-Dot Symbols The 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 9 Groups and Electron-Dot Symbols In a group, all the electron-dot symbols have the same number of valence (dots). Example: Atoms of elements in Group 2A (2) each have two valence. 10 2A (2) Be Mg Ca Sr Ba Periodic Table and Electron- Dot Symbols A. X is the electron-dot symbol for 1) Na 2) K 3) Al B. X is the electron-dot symbol of 1) B 2) N 3) P 11 12 2
Atomic Radius The atomic radius is the distance from the nucleus to the valence Atomic Radius within a Group The atomic radius increases going down each group of representative elements as the number of energy levels increases 13 14 Atomic Radius across a Period The atomic radius decreases going from left to right across a period as more protons increase the nuclear attraction for valence Select the element in each pair with the larger atomic radius. A. Li or K B. K or Br C. P or Cl 15 16 Ionization energy is the energy it takes to remove a valence electron Metals have 1-3 valence lower ionization energies 17 18 3
Nonmetals have 5-7 valence higher ionization energies Noble gases have complete octets (He has two valence ) the highest ionization energies in each period 19 20 Select the element in each pair with the higher ionization energy. A. Li or K B. K or Br C. P or Cl Metallic Character Elements with high metallic character lose their easily. Elements that are metals lose their easily. metalloids lose, but not as easily as metals. nonmetals do not easily lose their. 21 Sizes of Metal Atoms and Ions A positive ion has lost its valence is smaller than the corresponding metal atom (about half the size) Size of Sodium Ion The sodium ion Na + forms when the Na atom loses one electron from the third energy level is smaller than a Na atom 23 24 4
Sizes of Nonmetal Atoms and Ions A negative ion has a complete octet increases the number of valence is larger than the corresponding nonmetal atom (about twice the size) 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 a F atom 25 26 Electronegativity 1. Which is larger in each of the following? A. K or K + B. Al or Al 3+ C. S 2- or S 2. Which is smaller in each of the following? A. N 3- or N B. Cl or Cl - C. Sr 2+ or Sr Electronegativity is the relative ability of atoms to attract shared is higher for nonmetals, with fluorine as the highest with a value of 4.0 is lower for metals, with cesium and francium as the lowest with a value of 0.7 increases from left to right going across a period on the periodic table decreases going down a group on the periodic table 27 28 Some Electronegativity Values for Group A Elements Using the periodic table, predict the order of increasing electronegativity for the elements O, K, and C. 29 30 5