shapes of molecules Valence Shell Electron Pair Repulsion |VSEPR


The Shapes of Molecules (VSEPR Theory) 



The shapes of molecules are predicted and rationalize by Valence Shell 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)

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