![]() ![]() ![]() These four sp 3 hybridized electrons of carbon atoms bond with four hydrogen atom to form a methane molecule with tetrahedral geometry. For example, in CH4 molecule, the valence-shell electrons of carbon with same spin are most probably located at the vertices of a tetrahedron. According to Pauli, there is zero probability of finding two electrons with same spin at the same location and maximum probability of finding them as far apart as possible. The understanding of why electrons in molecules are found in pairs only came after the discovery of electron spin in 1926 and the later formulation of the Pauli principle. This arrangement leads to decrease in mutual repulsion, decrease in molecule's energy and increases its stability, which finally determines the molecular geometry. The main premise of VSEPR is that the valence electron pairs surrounding the central atom tend to repel each other until the distance between them is maximized. Moreover, the sharing of electron clouds strongly suggests the presence of covalent bonding between atoms.įigure 1: Localized concentrations of electronic charge of the furan (C4H4O) molecule (License: CC BY-SA 4.0 Attribution-Share Alike 4.0 Internationa). The circular red regions are those areas with high values of electron localization whilst orange cloudy regions are those areas with smaller values of electron localization. With increasing accuracy of X-ray crystallography, the studies of electron densities have provided important information about bonding in molecules and strong support for VSEPR theory.Ī 2D map of the molecular plane obtained from the topological analysis for ELF of a Furan (C 4H 4O) molecule defined by the C, H and O atom is presented in Fig. Therefore it is very sensitive to open shell or shared electron interactions. ![]() Electron localization function is related to the probability of finding another electron at that same point with the same spin. The insights of VSEPR theory are derived from topological analysis of the electron density of molecules such as electron localization function (ELF) and the quantum theory of atoms in molecules (QTAIM). This theory was purposed by Ronald Gillespie and Ronald Nyholm. Valence shell electron pair repulsion (VSEPR) theory is a model that tells about the three-dimensional geometry of a basically simple and symmetric molecule by accounting the number of electron pairs surrounding the central atom. Valence shell electron pair repulsion theory It consists of set of rules that can be used to look at a two-dimensional Lewis structure of a molecule and figure out the three-dimensional structure of the molecule. Valence shell electron pair repulsion (VSEPR) model can be used to determine the shape of a molecule or polyatomic ions. are intrinsically related to its molecular geometry. Various physical and chemical properties of a substance such as polarity, reactivity, magnetism, phase of matter, color, thermal properties, etc. More specifically it is determined by number of lone and bonded pairs of electrons. But, the molecular geometry is determined by the outermost electrons or valence electrons because these are the electrons involved in bonds formation. Atoms are surrounded by clouds of negatively charged electrons. ![]()
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