Molecular Geometry

1. Molecular Geometry Now we can use what we know about molecules from their lewis dot structures to determine their 3 dimensional shape in space. Today you will research what types of shapes molecules take in space and why. The site below gives a brief overview of some of the most popular molecular shapes and some of the properties that help to determine these shapes http://library.thinkquest.org/10429/low/geometry/geobody.htm

2. ValenceShellElectronPairRepulsionTheory Planar triangular Tetrahedral Trigonal bipyramidal Octahedral

3. VSEPR Theory • Based on Lewis structures we can know the shape or “geometry” of molecules • The theory that predicts geometry (based on Lewis structures) is abbreviated VSEPR • VSEPR (pronounced “vesper”) stands for Valence Shell Electron • Pair Repulsion • VSEPR, as the name suggests, predicts geometry based on the repulsion of electron pairs (in bonds or by themselves) • Electrons around the central nucleus repel each other. Thus, resulting structures have atoms maximally spread out.

4. VSEPR overview • The balloons represent electron clouds. At the end of each balloon will be a peripheral atom. The balloons meet at a central atom. • Each shape containing 2-6 peripheral atoms has a name • Sometimes the molecules are represented by AXY, where Y is the # of peripheral atoms • AX2 = linear • AX3 = planar triangular • AX4 = tetrahedral (tetra = 4 faces) • AX5 = trigonalbipyramidal (2 pyramids) • AX6 = octahedral (octa = 8 faces) Can you identify the correct shapefor the #’s of balloons above?

5. Ball and stick models showing molecular geometry Planar triangular Tetrahedral Trigonal bipyramidal Octahedral