Lewis StructuresA dot represents and electronA line represents two shared electronsObey octet rule as much as possibleDrawing Lewis structuresDetermine the number and type of atoms in the moleculeDetermine the number of total valence electronsPick a starting place (central atom)Try something obeying the octet rule!Formal Charge of an atom= # of valence e- - (# of unshared valence e- + ½ # of shared valence e-)ResonanceSome molecules cannot be represented with one single structure, so we draw several!Therefore when two or more valid Lewis Structures can be drawn for a molecule it is said to have resonanceSymmetry is a good indicator of resonanceChoosing the Best StructureMost stable resonance structures:Formal charges equal or close to zeroNegative formal charges on the more electronegative element*formal charge calculations for the resonance structure of N2OExample of Resonance: Co 2-, 3NCS-Lewis Structure Exceptions to the Octet RuleElectron Deficient atomsOdd-Electron AtomsExpanded Valence ShellsElectron Deficient atomsRelatively rate and occurs when there re fewer than 8 valence electrons around an atom in a moleculeBeryllium and BoronOdd-Electron AtomsMolecules in which the total number of valence electrons is oddExpanded Valence ShellsExpanded valence shells occur on ly with nonmetals form Period 3 or higherCHEM 111 1nd Edition Lecture 17 Outline of Last Lecture I. ElectronegativityII. Polar Covalent BondsIII. Bond PolarityIV. Electronegativity DifferencesOutline of Current Lecture II. ReviewIII. Resonance IV. Lewis Structure Exceptions to the Octet RuleCurrent LectureReview: Lewis Structures- A dot represents and electron- A line represents two shared electrons- Obey octet rule as much as possible Drawing Lewis structures- Determine the number and type of atoms in the molecule- Determine the number of total valence electrons- Pick a starting place (central atom)- Try something obeying the octet rule! Formal Charge of an atom= # of valence e- - (# of unshared valence e- + ½ # of shared valence e-)These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. ResonanceSome molecules cannot be represented with one single structure, so we draw several!Therefore when two or more valid Lewis Structures can be drawn for a molecule it is saidto have resonanceSymmetry is a good indicator of resonance Choosing the Best StructureMost stable resonance structures:Formal charges equal or close to zeroNegative formal charges on the more electronegative element*formal charge calculations for the resonance structure of N2O Example of Resonance: Co 2-, 3 NCS- Lewis Structure Exceptions to the Octet RuleElectron Deficient atomsOdd-Electron AtomsExpanded Valence Shells  Electron Deficient atomsRelatively rate and occurs when there re fewer than 8 valence electrons around an atom in a moleculeBeryllium and Boron Odd-Electron AtomsMolecules in which the total number of valence electrons is odd Expanded Valence ShellsExpanded valence shells occur on ly with nonmetals form Period 3 or