9-1 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 9 Models of Chemical Bonding

9-2 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Models of Chemical Bonding 9.1 Atomic Properties and Chemical Bonds 9.2 The Ionic Bonding Model 9.3 The Covalent Bonding Model 9.4 Bond Energy and Chemical Change 9.5 Between the Extremes: Electronegativity and Bond Polarity

9-3 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. A general comparison of metals and nonmetals. Figure 9.1

9-4 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Types of Chemical Bonding 1. Metal with nonmetal: electron transfer and ionic bonding 2. Nonmetal with nonmetal: electron sharing and covalent bonding 3. Metal with metal: electron pooling and metallic bonding

9-5 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 9.2 The three models of chemical bonding.

9-6 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lewis Electron-Dot Symbols For main group elements - Example: Nitrogen, N, is in Group 5A and therefore has 5 valence electrons. N:... : N.... N:.. : N... The A group number gives the number of valence electrons. Place one dot per valence electron on each of the four sides of the element symbol. Pair the dots (electrons) until all of the valence electrons are used.

9-7 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 9.4 Lewis electron-dot symbols for elements in Periods 2 and 3.

9-8 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. SAMPLE PROBLEM 9.1Depicting Ion Formation PLAN: SOLUTION: PROBLEM:Use partial orbital diagrams and Lewis symbols to depict the formation of Na + and O 2- ions from the atoms, and determine the formula of the compound. Draw orbital diagrams for the atoms and then move electrons to make filled outer levels. It can be seen that 2 sodiums are needed for each oxygen. 3s3p Na 3s3p Na 2s2p O 2s2p O 2- 2 Na + : Na + O. :... 2Na + + O 2- : : ::

9-9 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Electron configurations Li 1s 2 2s 1 Orbital diagrams Lewis electron-dot symbols +F 1s 2 2s 2 2p 5 Li + 1s 2 +F - 1s 2 2s 2 2p 6 Three ways to represent the formation of Li + and F - through electron transfer. Figure 9.5 Li 1s2s2p F 1s2s2p + Li + 1s2s2p F-F- 1s2s2p +. +F:: : Li. Li + +F - :: : :

9-10 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Periodic Trends in Lattice Energy Coulomb’s Law charge A X charge B electrostatic force  distance 2 energy = force X distance therefore charge A X charge B electrostatic energy  distance cation charge X anion charge electrostatic energy  cation radius + anion radius  H 0 lattice

9-11 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 9.7 Trends in lattice energy.

9-12 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 9.8 Electrostatic forcesand the reason ionic compounds crack.

9-13 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 9.9 Electrical conductance and ion mobility. Solid ionic compound Molten ionic compound Ionic compound dissolved in water

9-14 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Table 9.1 Melting and Boiling Points of Some Ionic Compounds Compoundmp ( 0 C)bp ( 0 C) CsBr Na I MgCl 2 KBr CaCl 2 NaCl LiF KF MgO >

9-15 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 9.10 Covalent bond formation in H 2.

9-16 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 9.11 Distribution of electron density of H 2.

9-17 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. back to previous slide Table 9.2

9-18 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 9.12 Internuclear distance (bond length) Internuclear distance (bond length) Internuclear distance (bond length) Internuclear distance (bond length) Bond length and covalent radius. Covalent radius 72 pmCovalent radius 114 pm Covalent radius 133 pm Covalent radius 100 pm

9-19 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Table 9.3

9-20 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. SAMPLE PROBLEM 9.2Comparing Bond Length and Bond Strength SOLUTION: PROBLEM:Using the periodic table, but not Tables 9.2 and 9.3, rank the bonds in each set in order of decreasing bond length and bond strength: (a) S - F, S - Br, S - Cl(b) C = O, C - O, C O PLAN:(a) The bond order is one for all and sulfur is bonded to halogens; bond length should increase and bond strength should decrease with increasing atomic radius. (b) The same two atoms are bonded but the bond order changes; bond length decreases as bond order increases while bond strength increases as bond order increases. (a) Atomic size increases going down a group. Bond length: S - Br > S - Cl > S - F Bond strength: S - F > S - Cl > S - Br (b) Using bond orders we get Bond length: C - O > C = O > C O Bond strength: C O > C = O > C - O

9-21 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 9.13 Strong covalent bonding forces within molecules Weak intermolecular forces between molecules Strong forces within molecules and weak forces between them.

9-22 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 9.14 Covalent bonds of network covalent solids.

9-23 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 9.15 The infrared (IR) spectra of diethyl ether and 2-butanol.

9-24 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 9.16 Using bond energies to calculate  H 0 rxn.  H 0 rxn =  H 0 reactant bonds broken +  H 0 product bonds formed  H 0 1 = + sum of BE  H 0 2 = - sum of BE  H 0 rxn Enthalpy, H BOND BREAKING BOND FORMATION

9-25 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 9.17 Using bond energies to calculate  H 0 rxn of methane. Enthalpy,H BOND BREAKING 4BE(C-H)= +1652kJ 2BE(O 2 )= + 996kJ  H 0 (bond breaking) = +2648kJ BOND FORMATION 4[-BE(O-H)]= -1868kJ  H 0 (bond forming) = -3466kJ  H 0 rxn = -818kJ 2[-BE(C O)]= -1598kJ

9-26 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. SAMPLE PROBLEM 9.3Calculating Enthalpy Changes from Bond Energies SOLUTION: PROBLEM: Use Table 9.2 (button at right) to calculate  H 0 rxn for the following reaction: CH 4 ( g ) + 3Cl 2 ( g ) CHCl 3 ( g ) + 3HCl( g ) PLAN:Write the Lewis structures for all reactants and products and calculate the number of bonds broken and formed. bonds brokenbonds formed

9-27 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. SAMPLE PROBLEM 9.3Calculating Enthalpy Changes from Bond Energies continued bonds brokenbonds formed 4 C-H = 4 mol(413 kJ/mol) = 1652 kJ 3 Cl-Cl = 3 mol(243 kJ/mol) = 729 kJ  H 0 bonds broken = 2381 kJ 3 C-Cl = 3 mol(-339 kJ/mol) = kJ 1 C-H = 1 mol(-413 kJ/mol) = -413 kJ  H 0 bonds formed = kJ 3 H-Cl = 3 mol(-427 kJ/mol) = kJ  H 0 reaction =  H 0 bonds broken +  H 0 bonds formed = 2381 kJ + (-2711 kJ) = kJ

9-28 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Table 9.4

9-29 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 9.20 The Pauling electronegativity (EN) scale.

9-30 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. SAMPLE PROBLEM 9.4Determining Bond Polarity from EN Values PLAN: SOLUTION: PROBLEM:(a) Use a polar arrow to indicate the polarity of each bond: N-H, F-N, I -Cl. (b) Rank the following bonds in order of increasing polarity: H-N, H-O, H-C. (a) Use Figure 9.19(button at right) to find EN values; the arrow should point toward the negative end. (b) Polarity increases across a period. (a) The EN of N = 3.0, H = 2.1; F = 4.0; I = 2.5, Cl = 3.0 N - HF - N I - Cl (b) The order of increasing EN is C < N < O; all have an EN larger than that of H. H-C < H-N < H-O

9-31 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 9.21 Electron density distributions in H 2, F 2, and HF.

9-32 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 9.22  EN Boundary ranges for classifying ionic character of chemical bonds.

9-33 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 9.23 Properties of the Period 3 chlorides.