Octahedral Complexes Octahedral moleculargeometry describes the shape of compounds wherein six atoms or groups of atoms or ligands are symmetrically arranged around a central atom, defining the vertices of an octahedron.
The term "octahedral" is used somewhat loosely by chemists, focusing on the geometry of the bonds to the central atom and not considering differences among the ligands themselves.
The premise of VSEPR is that the valence electron pairs surrounding an atom mutually repel each other, and will therefore adopt an arrangement that minimizes this repulsion, thus determining the moleculargeometry.
Therefore, although the oxygen atom is tetrahedrally coordinated, the bonding geometry (shape) of the H2O molecule is described as bent.
Linear Molecules A triatomic molecule of the type AX2 has its two bonding orbitals 180° apart, producing a molecule of linear geometry.
The bonding geometry will not be tetrahedral when the valence shell of the central atom contains nonbonding electrons.
An AX4E molecule (that is, a molecule in which the central atom is coordinated to four other atoms and to one nonbonding electron pair) will have a “see-saw” shape; substitution of more nonbonding pairs for bonded atoms reduces the triangular bipyramid coordination to even simpler molecular shapes.
If all of the electron pairs surrounding the central atom are shared with neighboring atoms, then the coordination geometry is the same as the moleculargeometry.
Both classes of geometry are named after the shapes of the imaginary geometric figures (mostly regular solid polygons) that would be centered on the central atom and would have an electron pair at each vertex.
Therefore, although the oxygen atom is tetrahedrally coordinated, the bonding geometry (shape) of the H2O molecule is described as bent .
Substitution of more nonbonding pairs for bonded atoms reduces the triangular bipyramid coordination to even simpler molecular shapes.
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