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Valence shell electron pair repulsion (VSEPR) theory (/ ˈ v ɛ s p ər, v ə ˈ s ɛ p ər / VESP-ər, [1]: 410 və-SEP-ər [2]) is a model used in chemistry to predict the geometry of individual molecules from the number of electron pairs surrounding their central atoms. [3]
Its structure was determined by both NMR spectroscopy and X-ray crystallography in 1963. [ 6 ] [ 7 ] The structure is square planar , as has been confirmed by neutron diffraction studies. [ 8 ] According to VSEPR theory , in addition to four fluoride ligands, the xenon center has two lone pairs of electrons.
Structure of cisplatin, an example of a molecule with the square planar coordination geometry. In chemistry, the square planar molecular geometry describes the stereochemistry (spatial arrangement of atoms) that is adopted by certain chemical compounds. As the name suggests, molecules of this geometry have their atoms positioned at the corners.
This would result in the geometry of a regular tetrahedron with each bond angle equal to arccos(− 1 / 3 ) ≈ 109.5°. However, the three hydrogen atoms are repelled by the electron lone pair in a way that the geometry is distorted to a trigonal pyramid (regular 3-sided pyramid) with bond angles of 107°.
According to VSEPR theory, T-shaped geometry results when three ligands and two lone pairs of electrons are bonded to the central atom, written in AXE notation as AX 3 E 2. The T-shaped geometry is related to the trigonal bipyramidal molecular geometry for AX 5 molecules with three equatorial and two axial ligands.
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Hybridisation helps to explain molecule shape, since the angles between bonds are approximately equal to the angles between hybrid orbitals. This is in contrast to valence shell electron-pair repulsion (VSEPR) theory, which can be used to predict molecular geometry based on empirical rules rather than on valence-bond or orbital theories. [11]
According to VSEPR theory, diethyl ether, methanol, water and oxygen difluoride should all have a bond angle of 109.5 o. [12] Using VSEPR theory, all these molecules should have the same bond angle because they have the same "bent" shape. [12] Yet, clearly the bond angles between all these molecules deviate from their ideal geometries in ...