Vsepr Theory

UNIT I

Geometry:
In VSEPRT, you will see two kinds of geometries Electron pair geometry: This geometry includes all the electron pairs (bp + lp) around the central atom. Molecular geometry: This includes only placement of atoms (bp) in the molecule. When there is no lone pair in molecules the two geometries are same.

PART C

VSEPR Theory
(Valence Shared Electron Pair Repulsion Theory)

Syllabus: Various rules under VSEPR theory to explain molecular geometry (following examples may be taken to explain various rules- BeCl2, BF3, CH4 , NH4+ , PCl5 , SF6, IF7, SnCl2 , NH3, H2O, SF4, ClF3, ICl2, ICl4, BrF5, XeF6, SOF4, COF2, PCl3, PBr3, PI3, F2O, H2S). Limitations of VSEPR theory.

How to draw VSEPR geometry?
To predict the shape of a covalent molecule, follow these steps: Step 1: Draw the Lewis structure of molecule. Make sure that you have drawn all the electron pairs around the central atom. Step 2: Count the number of electron pairs around the central atom. And determine the electron pair geometry using the following table. No. of electron pairs 2 3 4 5 Electron Pair Geometry Linear Trigonal planar Tetrahedral Trigonal bipyramidal Octahedral Pentagonal bipyramidal Bond angles 180° 120° 109.28° 120° & 90° 90° 72° & 90°

Introduction:
Shape of a covalent molecule can be predicted using the Valence Shell Electron Pair Repulsion theory. VSEPR theory says that the electron pairs in a molecule will arrange themselves around the central atom of a molecule so that the repulsion between them is as small as possible. In other words, the electron pairs arrange themselves so that they are as far apart as they can be. Depending on the number of electron pairs in the molecule, it will have a different shape.

Postulates of VSEPR theory:
1. The shape of a molecule depends upon the number of electron pairs (bonded or nonbonded) in valence shell of the central atom. 2. Pairs of electrons in the valence shell repel one another. 3. These pairs of electrons tend to