#electron geometry

ELECTRON GEOMETRY SERIES

The following examples illustrate the use of VSEPR theory to predict the molecular structures. Predicting Molecular Structures using VSEPR Theory For a particular number of electron pairs, the molecular structures for one or more lone pairs are determined based on modifications of the corresponding electron-pair geometry. The molecular structures are identical to the electron-pair geometries when there are no lone pairs present. In an octahedral arrangement with two lone pairs, repulsion is minimized when the lone pairs are on opposite sides of the central atom. In trigonal bipyramidal arrangements, repulsion is minimized when every lone pair is in an equatorial position. If more than one arrangement of lone pairs and chemical bonds is possible, choose the one that will minimize repulsions, remembering that lone pairs occupy more space than multiple bonds, which occupy more space than single bonds. Use the number of lone pairs to determine the molecular structure.Identify the electron-pair geometry based on the number of electron groups: linear, trigonal planar, tetrahedral, trigonal bipyramidal, or octahedral (As depicted in Figure 1, first column).A single, double, or triple bond counts as one region of electron density. Count the number of electron groups (lone pairs and bonds) around the central atom.Write the Lewis structure of the molecule or polyatomic ion.The following procedure uses VSEPR theory to determine the electron pair geometries and the molecular structures: VSEPR Theory for Determination of Electron Pair Geometries The bonding pairs stay in one plane and the lone pairs are placed on either side of this plane, minimizing the repulsion. The electron groups have an octahedral arrangement. The Lewis structure has six electron groups around the iodine atom: four bonding pairs and two lone pairs. These steps can again be used to determine the electron-pair geometry and molecular structure of the iodine tetrachloride anion. The lone pair occupies one of the equatorial positions, and the molecule is seesaw-shaped. The electron groups have a trigonal bipyramidal geometry. The Lewis structure of tellurium tetrachloride has five electron groups around the tellurium atom: four bonding pairs and one lone pair. The electron-pair and molecular geometries are identical because there are no lone pairs on the central atom, and carbon dioxide molecules are linear. The two-electron groups orient themselves on opposite sides of the central carbon atom with a bond angle of 180°. The Lewis structure of carbon dioxide shows the two-electron groups around the carbon atom-as each double bond counts as one electron group. The same protocol is used to predict the electron-pair geometry and molecular structure for carbon dioxide. The lone pair reduces the bond angle to less than 109.5°. However, because of the lone pair, the molecular geometry is trigonal pyramidal. The electron pair geometry is tetrahedral. Now determine the electron-pair geometry. Around phosphorus, there are four electron groups: three bonding pairs and one lone pair. Next, count the total number of electron groups on the central atom. The first step is to draw the Lewis structure of the molecule.

ELECTRON GEOMETRY SERIES

VSEPR theory helps to determine electron-pair geometries and molecular geometries.Ī series of steps is used to predict the geometry and bond angles of molecules, such as phosphorus trichloride.