VSEPR theory
Molecule type Shape Examples
AX 2 Bent VO 2
AX 3 Trigonal pyramidal CrO 3
AX 4 Tetrahedral TiCl 4
AX 5 Square pyramidal Ta ( CH 3 ) 5
AX 6 C 3v Trigonal prismatic W ( CH 3 ) 6
Valence shell electron pair repulsion theory, or VSEPR theory ( , ), is a model used in chemistry to predict the geometry of individual molecules from the number of electron pairs surrounding their central atoms. It is also named the Gillespie-Nyholm theory after its two main developers, Ronald Gillespie and Ronald Nyholm. The premise of VSEPR is that the valence electron pairs surrounding an atom tend to repel each other and will, therefore, adopt an arrangement that minimizes this repulsion, thus determining the molecule's geometry. Gillespie has emphasized that the electron-electron repulsion due to the Pauli exclusion principle is more important in determining molecular geometry than the electrostatic repulsion. VSEPR theory is based on observable electron density rather than mathematical wave functions and hence unrelated to orbital hybridisation, although both address molecular shape. While it is mainly qualitative, VSEPR has a quantitative basis in quantum chemical topology (QCT) methods such as the electron localization function (ELF) and the quantum theory of atoms in molecules (QTAIM).