shapes of molecules Valence Shell Electron Pair Repulsion |VSEPR
The Shapes of Molecules (VSEPR Theory) The shapes of molecules are predicted and rationalize by Va l ence Sh ell Electron Pair Repulsion (VSEPR) theory . The theory is based on minimizing the electrostatic repulsion between electron pairs, as first proposed by Sidgwick and Powell in 1940, then generalized by Gillespie and Nyholm in 1957. Determine the number of lone pairs on the central atom in the molecule, and add the number of bonded atoms (a.k.a. bonding domains) the steric number defines the electronic shape of the molecule by minimizing repulsion. For example a steric number of three gives a trigonal planar electronic shape. The angles between electron domains are determined primarily by the electronic geometry (e.g., 109.5° for a steric number of 4, which implies that the electronic shape is a tetrahedron) These angles are adjusted by the hierarchy of repulsions: (lone pair - lone pair) > (lone pair - bond) > (bond - bond)