Chapter 8 Bonding: General Concepts

Chapter 8 Table of Contents 8.1 Types of Chemical Bonds 8.2 Electronegativity 8.3 Bond Polarity and Dipole Moments 8.4 Ions: Electron Configurations and Sizes 8.5 Energy Effects in Binary Ionic Compounds 8.6Partial Ionic Character of Covalent Bonds 8.7The Covalent Chemical Bond: A Model 8.8Covalent Bond Energies and Chemical Reactions 8.9The Localized Electron Bonding Model 8.10Lewis Structures 8.11Exceptions to the Octet Rule 8.12Resonance 8.13Molecular Structure: The VSEPR Model

Chapter 8 Copyright © Cengage Learning. All rights reserved 3 Questions to Consider What is meant by the term “chemical bond”? Why do atoms bond with each other to form compounds? How do atoms bond with each other to form compounds?

Section 8.1 Types of Chemical Bonds Return to TOC Copyright © Cengage Learning. All rights reserved 4 1.To learn about ionic and covalent bonds and explain how they are formed 2.To learn about the polar covalent bond 3.To understand the nature of bonds and their relationship to electronegativity 4.To understand bond polarity and how it is related to molecular polarity Objectives 8.1 – 8.3

Section 8.1 Types of Chemical Bonds Return to TOC Copyright © Cengage Learning. All rights reserved 5 A. Types of Chemical Bonds Bond – force that holds groups of atoms together and makes them function as a unit Bond energy – energy required to break a chemical bond

Section 8.1 Types of Chemical Bonds Return to TOC Copyright © Cengage Learning. All rights reserved 6 A. Types of Chemical Bonds Ionic compound results when a metal reacts with a nonmetal. Results from a transfer of one or more e-s. Ionic Bonding (a) (b)

Sharing Electrons 20.2 Types of Bonds

Section 8.1 Types of Chemical Bonds Return to TOC Copyright © Cengage Learning. All rights reserved 8 A. Types of Chemical Bonds A covalent bond results when electrons are shared by nuclei Bond, Ionic Bond… Covalent Bonding

Section 12.1 Characteristics of Chemical Bonds

Section 8.1 Types of Chemical Bonds Return to TOC Copyright © Cengage Learning. All rights reserved 10 A. Types of Chemical Bonds A polar covalent bond results when electrons are shared unequally by nuclei Covalent Bonding –One atom attracts the electrons more than the other atom

Section 8.1 Types of Chemical Bonds Return to TOC Copyright © Cengage Learning. All rights reserved 11 B. Electronegativity Electronegativity – the relative ability of an atom in a molecule to attract shared electrons to itself –Increases from left to right across a period –Decreases down a group of representative elements –Why don’t noble gases have electronegativity values?

Section 8.1 Types of Chemical Bonds Return to TOC Copyright © Cengage Learning. All rights reserved 12 The Pauling Electronegativity Values

Section 8.1 Types of Chemical Bonds Return to TOC Copyright © Cengage Learning. All rights reserved 13 B. Electronegativity The polarity of a bond depends on the difference between the electronegativity values of the atoms forming the bond (partial charge, delta)

Section 8.1 Types of Chemical Bonds Return to TOC Copyright © Cengage Learning. All rights reserved 14 B. Electronegativity

Section 8.1 Types of Chemical Bonds Return to TOC Copyright © Cengage Learning. All rights reserved 15 B. Electronegativity The polarity of a bond depends on the difference between the electronegativity values of the atoms forming the bond If  electronegativity < 0.1, covalent (nonpolar) bond If 0.1 <  electronegativity < 1.7, Polar covalent bond If  electronegativity > 1.7, Ionic Bond Look on the back of Periodic Table to find electronegativity values. Classify the following Bonds: KF O 2 ICl Show the Partial Negative

Section 8.1 Types of Chemical Bonds Return to TOC Copyright © Cengage Learning. All rights reserved 16 B. Electronegativity For each of the following pairs of bonds, choose the bond that is more polar and assign the partial negative. H—P, H—C N—O, S—O O—F, O—I N—H, Si—H

Section 8.1 Types of Chemical Bonds Return to TOC Copyright © Cengage Learning. All rights reserved 17 C. Bond Polarity and Dipole Moments A dipole moment results when a polar molecule has a center for positive charge separate from a center for negative charge (partial charge, polar molecule, magnet) Lower Case delta. Greek letters?

Section 8.1 Types of Chemical Bonds Return to TOC Copyright © Cengage Learning. All rights reserved 18 The Effect of an Electric Field on Hydrogen Fluoride Molecules indicates a positive or negative fractional charge.

Section 8.1 Types of Chemical Bonds Return to TOC Copyright © Cengage Learning. All rights reserved 19 Polar Molecules

Section 8.1 Types of Chemical Bonds Return to TOC Copyright © Cengage Learning. All rights reserved 20 C. Greek Alphabet

Section 8.1 Types of Chemical Bonds Return to TOC Copyright © Cengage Learning. All rights reserved 21 C. Bond Polarity and Dipole Moments Water molecule dipole moment

Section 8.3 Bond Polarity and Dipole Moments Return to TOC Copyright © Cengage Learning. All rights reserved 22 Dipole Moment

Section 8.3 Bond Polarity and Dipole Moments Return to TOC Copyright © Cengage Learning. All rights reserved 23 No Net Dipole Moment (Dipoles Cancel)

Section 8.1 Types of Chemical Bonds Return to TOC Copyright © Cengage Learning. All rights reserved 24 C. Bond Polarity and Dipole Moments The polarity of water affects its properties –Magnetic properties cause water molecules to stick together and remain liquid at higher temperature –Permits ionic compounds to dissolve in it

Section 8.2 Electronegativity Return to TOC Copyright © Cengage Learning. All rights reserved 25 Concept Check If lithium and fluorine react, which has more attraction for an electron? Why? In a bond between fluorine and iodine, which has more attraction for an electron? Why?

Section 8.2 Electronegativity Return to TOC Copyright © Cengage Learning. All rights reserved 26 Concept Check What is the general trend for electronegativity across rows and down columns on the periodic table? Explain the trend.

Section 8.2 Electronegativity Return to TOC Copyright © Cengage Learning. All rights reserved 27 Exercise Arrange the following bonds from most to least polar: a) N–FO–FC–F b)C–FN–OSi–F a) C–F, N–F, O–F b) Si–F, C–F, N–O

Section 8.2 Electronegativity Return to TOC Copyright © Cengage Learning. All rights reserved 28 Concept Check Which of the following bonds would be the most polar without being considered ionic? Mg–O C–O O–O Si–O N–O

Section 8.3 Bond Polarity and Dipole Moments Return to TOC Copyright © Cengage Learning. All rights reserved 29 1.To learn about ionic and covalent bonds and explain how they are formed 2.To learn about the polar covalent bond 3.To understand the nature of bonds and their relationship to electronegativity 4.To understand bond polarity and how it is related to molecular polarity 5.Work Session: Page 382 #1, 3, 11, 23, 25 Objectives Review 8.1 – 8.3

Section 8.4 Ions: Electron Configurations and Sizes Return to TOC Copyright © Cengage Learning. All rights reserved 30 1.To learn about stable electron configurations 2.To learn to predict the formulas of ionic compounds 3.To learn about the structures of ionic compounds 4.To understand factors governing ionic size Objectives 8.4 – 8.8

Section 8.4 Ions: Electron Configurations and Sizes Return to TOC Copyright © Cengage Learning. All rights reserved 31 A. Stable Electron Configurations and Charges on Ions

Section 8.4 Ions: Electron Configurations and Sizes Return to TOC Copyright © Cengage Learning. All rights reserved 32 A. Stable Electron Configurations and Charges on Ions

Section 8.4 Ions: Electron Configurations and Sizes Return to TOC Copyright © Cengage Learning. All rights reserved 33 A. Stable Electron Configurations and Charges on Ions Atoms in stable compounds usually have a noble gas electron configuration –Metals lose electrons to reach noble gas configuration –Nonmetals gain electrons to reach noble gas configuration –Full valence electron orbitals are more stable than partly full valence orbitals. Think spin and overall balance.

Section 8.4 Ions: Electron Configurations and Sizes Return to TOC Copyright © Cengage Learning. All rights reserved 34 A. Stable Electron Configurations and Charges on Ions Chemical compounds are always electrically neutral They tend to resemble noble gas electron configurations Isoelectronic – having the same electron configurations Predicting Formulas of Ionic compounds

Section 8.4 Ions: Electron Configurations and Sizes Return to TOC Copyright © Cengage Learning. All rights reserved 35 B. Ionic bonding and Structures of Ionic Compounds Ions are packed together to maximize the attractions between ions Structures of Ionic Compounds

Section 8.4 Ions: Electron Configurations and Sizes Return to TOC Copyright © Cengage Learning. All rights reserved 36 B. Ionic bonding and Structures of Ionic Compounds Cations are always smaller than the parent atom Structures of Ionic Compounds Anions are always larger than the parent atom Why? Cations lose e-s, get smaller Anions gain e-s, get bigger

Section 8.4 Ions: Electron Configurations and Sizes Return to TOC Copyright © Cengage Learning. All rights reserved 37 B. Ionic bonding and Structures of Ionic Compounds Polyatomic ions work in the same way as simple ions –The covalent bonds hold the polyatomic ion together so it behaves as a unit Ionic Compounds Containing Polyatomic Ions

Section 8.4 Ions: Electron Configurations and Sizes Return to TOC Copyright © Cengage Learning. All rights reserved 38 Ionic Radii

Section 8.5 Energy Effects in Binary Ionic Compounds Return to TOC Copyright © Cengage Learning. All rights reserved 39 Born-Haber Cycle for NaCl

Section 8.7 The Covalent Chemical Bond: A Model Return to TOC Copyright © Cengage Learning. All rights reserved 40 Models Models are attempts to explain how nature operates on the microscopic level based on experiences in the macroscopic world.

Section 8.7 The Covalent Chemical Bond: A Model Return to TOC Copyright © Cengage Learning. All rights reserved 41 Fundamental Properties of Models 1.A model does not equal reality. 2.Models are oversimplifications, and are therefore often wrong. 3.Models become more complicated and are modified as they age. 4.We must understand the underlying assumptions in a model so that we don’t misuse it. 5.When a model is wrong, we often learn much more than when it is right.

Section 8.4 Ions: Electron Configurations and Sizes Return to TOC Copyright © Cengage Learning. All rights reserved 42 1.To learn about stable electron configurations 2.To learn to predict the formulas of ionic compounds 3.To learn about the structures of ionic compounds 4.To understand factors governing ionic size 5.Work Session: Page 383 #29, 35, 37, 41 Objectives Review 8.4 – 8.8

Section 8.9 The Localized Electron Bonding Model Return to TOC Copyright © Cengage Learning. All rights reserved 43 1.To learn to write Lewis structures 2.To learn to write Lewis structures for molecules with multiple bonds 3.To understand how symmetry affects molecular polarity 4.To write resonance Lewis structures Objectives 8.9 – 8.12

Section 8.9 The Localized Electron Bonding Model Return to TOC Copyright © Cengage Learning. All rights reserved 44 A. Writing Lewis Structures In writing Lewis structures we include only the valence electrons (Roman Numeral Group Number) Most important requirement –Atoms achieve noble gas electron configuration (octet rule, duet rule for H)

Section 8.9 The Localized Electron Bonding Model Return to TOC Copyright © Cengage Learning. All rights reserved 45 A. Writing Lewis Structures Bonding pairs are shared between 2 atoms Unshared pairs (lone pairs) are not shared and not involved in bonding H 2, Cl 2, Br 2, I 2

Section 8.9 The Localized Electron Bonding Model Return to TOC Copyright © Cengage Learning. All rights reserved 46 A. Writing Lewis Structures (page 355) Determine the TOTAL number of valence e-s from all atoms Draw a symmetrical skeleton structure- First atom (not H) is frequently the central atom– any atom bonded to > 1 other atom –Bonded atom – any atom bonded to a central atom Bonded atoms get e-s in pairs to fill their octet/duet. Use the remaining e-s in pairs to satisfy the octet rule for the central atom. Circle the octets! THINK SYMMETRY!

Section 8.9 The Localized Electron Bonding Model Return to TOC Copyright © Cengage Learning. All rights reserved 47 A. Writing Lewis Structure for H 2 O

Section 8.9 The Localized Electron Bonding Model Return to TOC Copyright © Cengage Learning. All rights reserved 48 A. Writing Lewis Structures HF NF 3 NH 3 CH 4 CF 4 CCl 4 PH 3 Circle the Octet CH 3 Cl H 2 S SiF 4 HCl

Section 8.9 The Localized Electron Bonding Model Return to TOC Copyright © Cengage Learning. All rights reserved 49 A. Writing Lewis Structures Write the Lewis Structures for the following polyatomic ions: SO 4 -2 NH 4 + ClO 4 - PH 4 + See the octet? OH - PO 4 -3 O 2 -2

Section 8.9 The Localized Electron Bonding Model Return to TOC Copyright © Cengage Learning. All rights reserved 50 B. Lewis Structures of Molecules with Multiple Bonds Single bond – covalent bond in which 1 pair of electrons is shared by 2 atoms Double bond – covalent bond in which 2 pairs of electrons are shared by 2 atoms Triple bond – covalent bond in which 3 pairs of electrons are shared by 2 atoms Annotated Rule For Lewis Dot Structures: If sharing 1 pair of e-s in a bond doesn’t fill the octet rule, try 2 pairs of e-s or 3 pairs of e-s.

Section 8.9 The Localized Electron Bonding Model Return to TOC Copyright © Cengage Learning. All rights reserved 51 B. Lewis Structures of Molecules with Multiple Bonds Write the Multiple Bond Lewis Structures for the following: O 2 N 2 CO NO + HCN (C is the central atom) C 2 H 4 (Ethene) C 2 F 4 (Teflon) SO 2 CN - CS 2 Molecular polarity and resonance

Section 8.9 The Localized Electron Bonding Model Return to TOC Copyright © Cengage Learning. All rights reserved 52 B. Lewis Structures of Molecules with Multiple Bonds –A molecule shows resonance when more than one Lewis structure can be drawn for the molecule –10 point Basketball Leader

Section 8.12 Resonance Return to TOC Copyright © Cengage Learning. All rights reserved 53 Actual structure is an average of the resonance structures. Electrons are really delocalized – they can move around the entire molecule.

Section 8.9 The Localized Electron Bonding Model Return to TOC Copyright © Cengage Learning. All rights reserved 54 B. Lewis Structures of Molecules with Resonance Write the Resonance Lewis Structures for the following: NO 3 - SO 3 ClO 3 - SO 2 CO 3 -2 O 3

Section 8.9 The Localized Electron Bonding Model Return to TOC Copyright © Cengage Learning. All rights reserved 55 B. Lewis Structures of Molecules –BrF –HI –Analyze the bonds to determine if the molecule will exhibit a dipole moment. Show the Orbital diagram, the octet, and the pairing.

Section 8.9 The Localized Electron Bonding Model Return to TOC Copyright © Cengage Learning. All rights reserved 56 1.To learn to write Lewis structures 2.To learn to write Lewis structures for molecules with multiple bonds 3.To understand how symmetry affects molecular polarity 4.To write resonance Lewis structures 5.Work Session: Page 384 # 67, 73 Pare Objectives Review 8.9 – 8.12

Section 8.13 Molecular Structure: The VSEPR Model Return to TOC Copyright © Cengage Learning. All rights reserved 57 VSEPR

Section 8.13 Molecular Structure: The VSEPR Model Return to TOC Copyright © Cengage Learning. All rights reserved 58 VSEPR: Two Electron Pairs

Section 8.13 Molecular Structure: The VSEPR Model Return to TOC Copyright © Cengage Learning. All rights reserved 59 VSEPR: Three Electron Pairs

Section 8.13 Molecular Structure: The VSEPR Model Return to TOC Copyright © Cengage Learning. All rights reserved 60 VSEPR: Four Electron Pairs

Section 8.13 Molecular Structure: The VSEPR Model Return to TOC Copyright © Cengage Learning. All rights reserved 61 VSEPR: Iodine Pentafluoride

Section 8.13 Molecular Structure: The VSEPR Model Return to TOC Copyright © Cengage Learning. All rights reserved 62 Arrangements of Electron Pairs Around an Atom Yielding Minimum Repulsion

Section 8.13 Molecular Structure: The VSEPR Model Return to TOC Copyright © Cengage Learning. All rights reserved 63 Arrangements of Electron Pairs Around an Atom Yielding Minimum Repulsion

Section 8.13 Molecular Structure: The VSEPR Model Return to TOC Copyright © Cengage Learning. All rights reserved 64 Structures of Molecules That Have Four Electron Pairs Around the Central Atom

Section 8.13 Molecular Structure: The VSEPR Model Return to TOC Copyright © Cengage Learning. All rights reserved 65 Structures of Molecules with Five Electron Pairs Around the Central Atom