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.

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

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

Periodic Table and Valence Electrons

Learning Check Identify the number of valence electrons for each of the following: 1. O A. 4 B. 6 C. 8 2. Al A. 13 B. 3 C. 1 3. Cl A. 2 B. 5 C. 7

Solution Identify the number of valence electrons for each of the following: 1. O B. 6 2. Al B. 3 3. Cl C. 7

Learning Check Identify the number of valence electrons for each of the following: 1. Calcium A. 1 B. 2 C. 3 2. Group 6A (16) A. 2 B. 4 C. 6 3. Tin A. 2 B. 4 C. 14

Solution Identify the number of valence electrons for each of the following: 1. Calcium B. 2 2. Group 6A (16) C. 6 3. Tin B. 4

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

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

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.

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:

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 ·

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

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

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.

Atomic Radius

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

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.

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.

Ionization Energy and Valence Electrons

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

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.

Metallic Character

Periodic Table Trend Summary

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

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.