WWU CHEM 121 - Chapter 9 Models of Chemical Bonding

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Slide 1Slide 2Sodium ChlorideSlide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Figure 9.11: Potential-energy curve for H2.Slide 13Slide 14Figure 9.10: The electron probability distribution for the H2 molecule.Slide 16Slide 17Slide 18Slide 19Figure 9.14: The HCl molecule.Slide 21Figure 9.12: Molecular model of nitro-glycerin.Slide 23Slide 24Figure 9.9: Model of CHI3 Courtesy of Frank Cox.Slide 26Slide 27Slide 28Slide 29A model of ethylene.A model of acetylene.A model of COCl2.Slide 33Slide 34A model of SCl2.Figure 9.16: Delocalized bonding in sodium metal.Model of CO32-Slide 38Slide 39Slide 40Conceptual Problem 9.103Slide 42Figure 9.15: Electronegatives of the elements.Slide 44Slide 45Slide 46Slide 47Slide 48Slide 49Slide 50Chapter #9 - Models of Chemical Bonding9.1) Atomic Properties and Chemical Bonds9.2) The Ionic Bonding Model9.3) The Covalent Bonding Model9.4) Between the Extremes: Electronegativity and Bond Polarity9.5) An Introduction to Metallic BondingSodium ChlorideDepicting Ion Formation with OrbitalDiagrams and Electron Dot Symbols - IProblem: Use orbital diagrams and Lewis structures to show the formation of magnesium and chloride ions from the atoms, and determine the formula of the compound.Plan: Draw the orbital diagrams for Mg and Cl. To reach filled outer levels Mg loses 2 electrons, and Cl will gain 1 electron. Therefore we need two Cl atoms for every Mg atom.Solution:2 ClMg+2 + 2 Cl-Mg+Mg + ..ClCl..............Mg+2 + 2 Cl........Depicting Ion Formation from OrbitalDiagrams and Electron Dot Symbols - IIProblem: Use Lewis structures and orbital diagrams to show the formation of potassium and sulfide ions from the atoms, and determinethe formula of the compound.Plan: Draw orbital diagrams for K and S. To reach filled outer orbitals,sulfur must gain two electrons, and potassium must lose one electron.Solution:2 KS2 K+ + S - 2+KK..+ S............2 K+ + S..2 -Three Ways of Showing the Formation ofLi+ and F - through Electron TransferLewis Electron-Dot Symbols for Elements in Periods 2 & 3The Reaction between Na and Br to Form NaBrThe ElementsThe Reaction!Vaporizing an Ionic CompoundMelting and Boiling Points of Some Ionic CompoundsCompound mp( oC) bp( oC)CsBr 636 1300NaI 661 1304MgCl2 714 1412KBr 734 1435CaCl2 782 >1600NaCl 801 1413LiF 845 1676KF 858 1505MgO 2852 3600Figure 9.11: Potential-energy curve for H2.Covalent Bonding in Hydrogen, H2Figure 9.10: The electron probability distribution for the H2 molecule.Covalent bondsanimationhttp://wine1.sb.fsu.edu/chm1045/notes/Bonding/Covalent/Bond04.htmhttp://www.chem.ox.ac.uk/vrchemistry/electronsandbonds/intro1.htmFor elements larger than Boron, atoms usually react todevelop octets by sharing electrons. H, Li and Be striveto “look” like He. B is an exception to the noble gas paradigm.It’s happy surrounded by 6 electrons so the compound BH3 is stable.Try drawing a Lewis structure for methane.Draw Lewis dot structures for the halogens.Try oxygen and nitrogen.Notice that these all follow the octet rule!These also follow the octet rule!Bond Lengths and Covalent RadiusFigure 9.14: The HCl molecule.Fig. 9.20The Charge Density of LiFFigure 9.12: Molecular model of nitro-glycerin. What is the formula for thiscompound?Rules for drawing Lewis structures1. Count up all the valence electrons2. Arrange the atoms in a skeleton3. Have all atoms develop octets (except those around He)Make some Lewis Dot Structures with other elements:SiH4NH3H2OC2H6C2H6OCH2OFigure 9.9: Model of CHI3Courtesy of Frank Cox. CH3IMake some Lewis Dot Structures with other elements:CH4 NH3H2OC2H6C2H6OCH2OLook at all these structures and make some bonding rules:The normal number of bonds that common elements make in covalent structures.Element # BondsCNOH, HalogensElement # BondsC 4N 3O 2H, Halogens 1Rules for drawing Lewis structures1. Count up all the valence electrons2. Arrange the atoms in a skeleton3. Have all atoms develop octets (except those around He)4. Satisfy bonding preferences!A model of ethylene.A model of acetylene.A model of COCl2.A model of SCl2.Figure 9.16: Delocalized bonding in sodium metal.Model of CO32-The Relation of Bond Order,Bond Length and Bond EnergyBond Bond Order Average Bond Average Bond Length (pm) Energy (kJ/mol)C O 1 143 358C O 2 123 745C O 3 113 1070C C 1 154 347C C 2 134 614C C 3 121 839N N 1 146 160N N 2 122 418N N 3 110 945Table 9.4Conceptual Problem 9.103Fig. 9.14Figure 9.15: Electronegatives of the elements.The Periodic Table of the Elements2.10.9 1.50.9 1.20.8 1.0 1.30.80.70.71.00.91.5 1.6 1.61.5 1.81.21.11.8 1.8 1.9 1.61.4 1.61.51.81.71.91.92.2 2.22.22.22.21.92.41.71.92.0 2.5 3.0 3.54.0HeNeAr1.5 1.8 2.1 2.5 3.01.6 1.8 2.0 2.4 2.8 KrXeRn2.52.12.21.92.01.91.81.71.81.81.1 1.1 1.1 1.11.31.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.21.31.5 1.7 1.3 1.3 1.3 1.3 1.3 1.3 1.31.3 1.50.91.3 2.2Electronegativity1.1Th Pa U NpNo Lr1.3Ce Pr Nd Pm Yb LuFig. 9.16Fig. 9.17Determining Bond Polarity from Electronegativity ValuesProblem: (a)Indicate the polarity of the following bonds with a polarity arrow: O - H,


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WWU CHEM 121 - Chapter 9 Models of Chemical Bonding

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