Christopher G. Hamaker, Illinois State University, Normal IL © 2008, Prentice Hall Chapter 10b Periodic Trends INTRODUCTORY CHEMISTRY INTRODUCTORY CHEMISTRY Concepts & Connections Fifth Edition by Charles H. Corwin

Chapter 6 2 The periodic law states that the properties of elements recur in a repeating pattern when arranged according to increasing atomic number. The arrangement of the periodic table means that the physical properties of the elements follow a regular pattern The Periodic Law

Chapter 6 3 Not all properties can be predicted by their position on the periodic table…we can predict Atomic Size Ion Size Ionization Energy Electronegativity Periodic Trends

Chapter 6 4 “Shielding” Shielding is an effect felt by valence (outer) electrons. Layers of core (inner) electrons “shield” or protect the outer electrons from the nucleus- so they feel less of an attraction to the nucleus. Electrons in the same valence shell do not shield one another

Chapter 6 5 This figure shows the atomic radii of the main group elements. The general trend in atomic radius applies to the main group elements, not the transition elements. Atomic Radius

Chapter 6 6 Atomic Radius We can look at the size of atoms, or their atomic radius. There are two trends for atomic radii: Atomic radius increases as you go down a group. Atomic radius decreases as you go left to right across a period.

Chapter 6 7 Atoms get larger as you go down a column because 3 things occur: – there are more energy levels between outer e- and nucleus –distance from the nucleus increases –increased amount of shielding Atomic radius decreases as you travel left to right across the periodic table because of the increased nuclear effect. (the number of protons in the nucleus increases with no additional shielding) As the number of protons increases, the nucleus pulls the electrons closer and reduces the size of the atom. Atomic Radius– the “Why”

Chapter 6 8 The ionization energy of an atom is the amount of energy required to remove an electron in the gaseous state. In general, the ionization energy decreases as you go from the top to the bottom in a group. In general, the ionization energy increases as you go from left to right across a period of elements. The closer the electron to the nucleus, the more energy is required to remove the electron. Ionization Energy

Chapter 6 9 Figure shows the trend for the first ionization energy of the elements. Ionization Energy Trend

Chapter 6 10 Sizes of Ions Cations (metal ions) are smaller than their parent atoms: –The outermost electron is removed and repulsions between electrons are reduced.

Chapter 6 11 Sizes of Ions Anions (nonmetal ions) are larger than their parent atoms” –Electrons are added and repulsions between electrons are increased.

Chapter 6 12 Sizes of Ions Ions increase in size as you go down a column: –This increase in size is due to the increasing energy levels

Chapter 6 13 Sizes of Ions Ionic size decreases across a period due to an increasing nuclear effect.

Chapter 6 14 Each element has an innate ability to attract valence electrons. Electronegativity is the ability of an atom to attract electrons in a chemical bond. Linus Pauling devised a method for measuring the electronegativity of each of the elements. Fluorine is the most electronegative element. Electronegativity

Chapter 6 15 Chapter Electronegativity increases as you go left to right across a period. Electronegativity increases as you go from bottom to top in a family. Electronegativity

Chapter 6 16 The electronegativity of H is 2.1; Cl is 3.0. Since there is a difference in electronegativity between the two elements (3.0 – 2.1 = 0.9), the bond in H – Cl is polar. Since Cl is more electronegative, the bonding electrons are attracted toward the Cl atom and away from the H atom. This will give the Cl atom a slightly negative charge and the H atom a slightly positive charge. Electronegativity Differences