What we are going to learn • How the number of bonds and lone pairs affect the geometry of molecules. (VSEPR) • How the geometries work with polarity to make a dipole moment. • Two theories of bonding • Valence Bond Theory: Atomic orbital hybridization. • Molecular orbital theory.
VSEPR:Valence Shell Electron-Pair Repulsion • Basic Principle: Electrons are negatively charged, they want to stay as far away from each other as possible. • Electron pairs show the most repulsion. • Single bonds can be treated the same as double and triple bonds.
Some Definitions • Steric Number: # bonds+# electron pairs • Coordination Number: number of bonded atoms Steric #: 4 Coord. #:3 Steric #: 5 Coord. #:5 Steric #: 6 Coord. #:5
Some (more) Definitions • Electron geometry: geometry including if you “saw” electron pairs • Molecular geometry: geometry where you don’t “see” electron pairs • Bond angle: angle between bonds. EG:Tetrahedral MG: Trig. pyramidal EG:Trig. bipyramidal MG: Trig. bipyramidal EG:Octahedral MG: Square Pyramidal
Pull out your worksheet, candy and toothpicks! Thanks to http://www.chemmybear.com/shapes.html for all animations on following slides!
Steric Number 3 Examples: SO3, BF3, CO32- Examples: SO2, CCl2
Steric Number 4 Examples: CH4, SiH4, PO4 Examples: NH3, PI3 Examples: H2O, OF2
Steric Number 5 Examples: PCl5, SbF5 Examples: TeCl4, SF4 Examples: ClF3, SeO32- Examples: I3-, XeF2
Steric Number 6 Examples: XeF4, ClF4- Examples: IF5, BrF5 Examples: SF6, Mo(CO)6
Going Back to Lewis Structures we did previously: Which bonds are polar?