Chem 121 1st Edition Lecture 15 Outline of Last LectureI. ResonanceII. Lewis Structures of Polyatomic Ions- ProceduresIII. Formal ChargeIV. Exceptions to the Octet Rule Outline of Current Lecture I. Molecular Structure: VSEPR (Valence Shell Electron Pair Repulsion) Model Current LectureVSEPRVSEPR Theory: minimum repulsion electron groups stay as far away as possible- 5 common electron groups (E.G.) arrangementso Linear Angle: 180 degreeso Trigonal planar Angle: 120 degreeso Tetrahedral Angle: 109.5 degreeso Trigonal bipyramidal Angles: 180, 120, 90 degreeso Octahedral Angle: 90 degrees- Same E.G. arrangement  different molecular shape- Lone (unshared, nonbonding) pair cannot be detected- Draw a valid Lewis dot structure- Focus on electron groups (or pairs) around the central atomo Lone/unshared pair: each lone pair counted as one electron pairo Bonding/shared pair: each bond counted as one electron pairo Treat each multiple bond as one single electron groupo Single electron (radical): counted as one electron group- Repulsion between electron groupo Electron groups have the same type of chargeso Stay as far apart from each other as possibleo Avoid <90 degree angles between electron groups- Molecular shapeo Relative position of the atoms in a molecule/iono Arrangement of atomsThese 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.- Bond angleo Angle formed by the nuclei of two surrounding atoms with the central atoms- 2 electron groups- linear- Symbol: Ax2- Electron groups on central atomo Lone Pair (L.P.): The more space required, the greater repulsion No atom at the other end to retrain the size Electrons in a lone pair repel themselves Stay on opposite sides of the central atom Occupies the most space around central atom Most repulsion effect squeeze bond angle by ~2 degreeso Multiple Bonds More electron groups in bonding – more space Stronger repulsion than single bonding pairs Repulsion: triple > double > singleo Repulsion Effect among electron clouds Lone pair > triple bond > double bond > single bond > single electron- 3 electron groups- Trigonal planar (E.G. Arrangement)o Molecular shapes Trigonal planar (AX3): Same E.G. arrangement when # L.P = 0 Bent (V-Shape)(AX2E): Derived from E.G. arrangement if # L.P does not = 0- 4 electron groups- tetrahedral (E.G. Arrangement)o Molecular shapes: o Tetrahedral (AX4): Same arrangement when # L.P = 0o Trigonal pyramidal (AX3E)o Bent (V-Shape)- 5 electron groups- Trigonal bipyramido Trigonal bipyramidal (AX5)o Seesaw (AX4E): Lone pair occupies equatorial positiono T-Shape (AX3E2)o Linear (AX2E3)- 6 electron groups- octahedral (E.P. Arrangement)o Octahedral (AX6)o Square pyramidal (AX5E)o Square Planar (AX4E2)General Procedures- Draw a valid Lewis dot structureo Determine the total valence electronso Set atoms, especially the central atomo Distribute electronso Octet for central atom- Determine molecule’s shape using VSEPR theoryo Count electron groups on central atom # of bonds # of lone pairso FIRST: determine electron group arrangemento Start with the chosen electron group arrangement, determine the molecular shape depending on the number of lone pair(s)- Electrons carry negative charge- All about predicting the molecular shape of the molecule- Electron arrangement: All electron groups- Molecular Shape: All electron groups and atoms at the end of the electron