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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]
According to the VSEPR theory of molecular geometry in chemistry, which is based on the general principle of maximizing the distances between points, a square antiprism is the favoured geometry when eight pairs of electrons surround a central atom. One molecule with this geometry is the octafluoroxenate(VI) ion (XeF 2−
This shape has D 4d symmetry and is one of the three common shapes for octacoordinate transition metal complexes, along with the dodecahedron and the bicapped trigonal prism. [2] [3] Like with other high coordination numbers, eight-coordinate compounds are often distorted from idealized geometries, as illustrated by the structure of Na 3 TaF 8.
The point group symmetry involved is of type C 4v. The geometry is common for certain main group compounds that have a stereochemically -active lone pair , as described by VSEPR theory . Certain compounds crystallize in both the trigonal bipyramidal and the square pyramidal structures, notably [Ni(CN) 5 ] 3− .
This shape has D 2d symmetry and is one of the three common shapes for octacoordinate transition metal complexes, along with the square antiprism and the bicapped trigonal prism. [1] [2] One example of the dodecahedral molecular geometry is the Mo(CN) 4− 8 ion. [2]
Structure of iodine heptafluoride, an example of a molecule with the pentagonal-bipyramidal coordination geometry.. In chemistry, a pentagonal bipyramid is a molecular geometry with one atom at the centre with seven ligands at the corners of a pentagonal bipyramid.
Structure of boron trifluoride, an example of a molecule with trigonal planar geometry.. In chemistry, trigonal planar is a molecular geometry model with one atom at the center and three atoms at the corners of an equilateral triangle, called peripheral atoms, all in one plane. [1]
The parallelepiped with D 4h symmetry is known as a square cuboid, which has two square faces and four congruent rectangular faces. The parallelepiped with D 3d symmetry is known as a trigonal trapezohedron, which has six congruent rhombic faces (also called an isohedral rhombohedron). For parallelepipeds with D 2h symmetry, there are two cases: