A180EEAEEE120AEEEE109.5AEEEEE90120equatorialpositionsaxialpositionAEEEEEE90Predicting Molecular Shape and Bond AnglesThe Lewis Structure of a molecule or ion shows only the placement of valence electrons. Note thatthe Lewis Structure does not give information on the three-dimensional shape of the molecule or ion.VSEPR theory (Valence Shell Electron Pair Repulsion ) must be used to predict the three-dimensionalshape of a molecule or ion. To use VSEPR theory, follow the steps outlined below:1. Draw a correct Lewis Structure for the molecule or ion.2. Count up the total number of regions of electron density surrounding the central atom (this includes both bonding and nonbonding pairs of electrons).3. Arrange the regions of electron density in one of the five arrangements shown below.Note: Since the regions of e- density are negatively charged (and therefore repel eachother), they will adopt a geometry in which they are located as far apart as possible.Total # Electron Arrangement Angle Between Pairs of Electron Pairs Electron Pairs 2 Linear 180/ 3 Trigonal Planar 120/ 4 Tetrahedral 109.5/ 5 Trigonal 90/, 120/ (180/)Bipyramidal 6 Octahedral 90/ (180/)4. The Molecular Shape is the resulting arrangement of the atoms in the moleculeor ion. The various molecular shapes are tabulated on the next page.VSEPR Theory Summary# Regions of # Regions of # Regions of Arrangement of MolecularFormula electron density bonding e- pairs nonbonding e- pairs regions of e- density ShapeAX22 2 0 linear linearAX33 3 0 trigonal planar trigonal planarAX2U13 2 1 trigonal planar bentAX44 4 0 tetrahedral tetrahedralAX3U14 3 1 tetrahedral trigonal pyramidalAX2U24 2 2 tetrahedral bentAX55 5 0 trigonal bipyramidal trigonal bipyramidalAX4U15 4 1 trigonal bipyramidal see-saw shapedAX3U25 3 2 trigonal bipyramidal T-shapedAX2U35 2 3 trigonal bipyramidal linearAX66 6 0 octahedral octahedralAX5U16 5 1 octahedral square pyramidalAX4U26 4 2 octahedral square planarKeyA = central atomX = bonding region of electron densityU = nonbonding region of electron density (i.e. lone pairs)Be180ClFBe180ClClPolarity of Molecules and IonsA polar molecule is one where the center of positive and negative charge (partial charge) does not coincide.One end of the molecule or ion has a permanent partial positive charge while the other end of the molecule has apermanent partial negative charge. Polar molecules are obtained when the vector sum of the bond dipoles is nonzero.Nonpolar molecules are obtained when the center of positive and negative charge coincide. Nonpolar molecules areobtained when the vector sum of bond dipoles is zero. A molecule or ion with polar covalent bonds can be eitherpolar or nonpolar depending on the three-dimensional arrangement of the atoms. An easy way to tell if a moleculeis polar or nonpolar is to look at the symmetry of the molecule. Highly symmetric molecules are nonpolar whileunsymmetric molecules are generally polar.For example BeCl2 is nonpolar while BeFCl is polar. Both molecules have a linear molecular shape butBeCl2 is highly symmetric while BeFCl is unsymmetric. (See the diagram below)Sum of bond dipoles equal zero. Sum of bond dipoles is nonzero because F moreHighly symmetric molecular shape. electronegative than Cl. Unsymmetric molecular shape.NONPOLAR POLARTo determine whether or not a molecule or ion is polar, perform the following steps:1. Draw the Lewis Structure.2. Predict the Molecular Shape using VSEPR theory.3. If the molecular shape is symmetric, then the molecule is nonpolar. If the molecular shape isunsymmetric, then the molecule is polar.Example: Is SF4 polar or