Warm up Draw lewis structures for the compounds below: CF4 BF3 CO2

The 3D Shapes of Molecules VSEPR Theory The 3D Shapes of Molecules

VSEPR Theory Valence Shell Electron Pair Repulsion Predicts the 3D geometry of molecules The structure of covalent bonds around an atom is determined by minimizing electron-pair repulsions Get electrons as far apart as possible! Base structure depends on how many electron domains there are in the molecule Molecule geometry depends on how many bonding pairs there are

Bond Lengths Bond length increases as atomic radius increases Bond length decreases with multiple bonds: Single > Double > Triple Remember: Bond strength increases as bond length decreases

Turn to back of your notes We will finish the front in a little bit!

4 Electron Domains CF4 NCl3 H2Se Tetrahedral: CF4 Trigonal Pyramidal: NCl3 Bent: H2Se H2Se

3 Electron Domains BF3 Trigonal Planar: BF3 Bent: NOH NOH

2 Electron Domains All diatomic compounds are linear C2H2 Linear: C2H2 All diatomic compounds are linear Most compounds with double or triple bonds are linear

Bond Angles Shape Angle of Bond Tetrahedral (4 e- regions) 109.5° CF4 Trigonal Pyramidal (4 e- regions) <109.5° NCl3 Bent (4 e- regions) <109.5° H2Se Trigonal Planar(3 e- regions) 120° BF3 Linear (2 e- regions) 180° NOH

Bond Polarity Some molecules that have polar bonds are nonpolar! If the dipole arrows cancel each other out, then the molecule does not have an overall dipole and will be nonpolar. Examples: CO2, BF3, CF4 Example: CO2, BF3, CF4

Warm-Up Draw the Lewis dot structures (see your notes) WITH dipole arrows for the following 3 molecules. Carbon Dioxide Boron Trifluoride Carbon Tetrafluoride