Molecular Geometry Chart Molecular Geometry Chart Molecular geometry or molecular structure is the three-dimensional arrangement of the atoms that constitute a molecule. It determines several properties of a substance including its reactivity, polarity, phase of matter, color, magnetism, and biological activity. The angles between bonds that an atom forms depend only weakly on the rest of molecule, i.e. they can be understood as approximately local and hence transferable properties. Central Atom Molecular Geometry The electronic geometry for a given number of electron pairs surrounding a central atom is always the same. That number of electron pair will distribute themselves in the same way to maximize their separation. The same thing cannot be said for molecular geometry. The molecular shape depends not only on the electronic geometry but also on the number of the electron pairs that are shared. When the central metal atom is surrounded with five pairs of electrons the electronic geometry is trigonal bi pyramidal.
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If all the electron pairs are shared the molecular geometry will also be trigonal bi pyramidal. An example for such a molecule is PF5. If one of the pairs of electrons are not shared then the molecular shape is called distorted tetrahedron which sometimes is also called as seesaw. An example of a molecule with trigonal bi pyramidal electronic geometry and the molecular shape as distorted tetrahedron is SF4. In this molecule SF4, there are five electron pairs which should lead to trigonal bi pyramidal structure. However, out of the five electron pairs, one is a lone pair. This lone pair could occupy an axial position or an equatorial position. SF4Molecular Geometry Hybridization of an atom depends on the steric number that is number of atoms attached with central atom and lone pairs of electrons present on it. There are two ways in which the chemical bond of SF4 can be explained. One is the new hybridization using one 3d orbital of the sulfur atom with the normal 3 sp3, resulting in the formation of the five coordinate bonds sp3d required for the decet. The other is the resonance among the conceivable ionic forms, that is in case of SF4 it should be a resonance hybrid of S+F3.F-, SF4, and so on. Therefore, S atom in SF4 is sp3d hybridized. The fifth sp3d orbital accommodates a lone pair of electrons. Hence SF4 is not square planar. The most stable arrangement of SF4 is when lone pair is in axial position it would be 90o from the three closest other pairs and 180o from the other axial pair.
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If it were an equatorial position, only the two axial pairs would be at 90o from the lone pair, and the two equatorial pairs would be farther away at 120o. The lone pair would, therefore, be less crowded in an equatorial position. The four F atoms then occupy the remaining four positions. The resulting arrangement is the seesaw arrangement. For instance the lone pair - bond pair repulsion in the seesaw molecules SF4 causes distortion of the axial; S-F bonds away from the lone pair to an angle of 177o, the two equatorial S-F bonds, ideally at 120o, move much closer to an angle of 101.6o. The arrangement is shown below.
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Published on Sep 10, 2012