2Shapes of ABnMolecules (cont’d)There are additional possible molecular geometries.For n = 2:For n = 3:For n = 4:For n = 5:How can the shape be predicted?VSEPROne of the first (& simplest) theories describing molecular geometry is VSEPR–Valence Shell Electron Pair RepulsionThe theory uses the concept that like charges repel to explain the geometry observed in molecules. Electron pairs (in either bonds or lone pairs) are arranged to be as far apart as possible around the atom.VSEPR (cont’d)We need to know the number of electron pairs, so if necessary draw the Lewis structure.Determine the number of:1) 2) 3) 4)
3Types of Geometry•Electron domain geometry is the arrangement of bonding and nonbonding electron pairs around the central atom.•Molecular geometry is the arrangement of the bonded atoms around the central atom.•The distinction is very important!VSEPR (cont’d)Two pair of e-: BeCl2VSEPR (cont’d)Double or triple bonds are considered one domain as well.HCNH-C≡N:This molecule is linear. The triple bond is one domain and the single bond is a second domain.What is the expected geometry of CO2?
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