Definition of molecular geometry
The spatial arrangement of atoms in a molecule.
Examples of molecular geometry in the following topics:
- Tetrahedral ComplexesIn tetrahedral molecular geometry, a central atom is located at the center of four substituent atoms, which form the corners of a tetrahedron.
- This geometry is widespread, particularly for complexes where the metal has d0 or d10 electron configuration.
- For more information on octahedral complexes, see the unit on Octahedral Geometries.Square Planar ComplexesIn square planar molecular geometry, a central atom is surrounded by constituent atoms, which form the corners of a square on the same plane.
- The geometry is prevalent for transition metal complexes with d8 configuration.
- Therefore, the crystal field splitting diagram for square planar geometry can be derived from the octahedral diagram.
- Molecular size varies depending on the number of atoms that make up the molecule.
- The elemental composition of a molecule can be exactly represented by its molecular formula, which provides the exact number of atoms that are in the molecule.
- The molecular geometry and composition determine the reactivity and other properties of a molecule.
- Octahedral ComplexesOctahedral molecular geometry 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.
- An example of an octahedral compound is molybdenum hexacarbonyl, Mo(CO)6.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.
- This causes the molecular geometry to be different from the coordination geometry, which remains tetrahedral.
- If all of the electron pairs surrounding the central atom are shared with neighboring atoms, then the coordination geometry is the same as the molecular geometry.
- 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.
- 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 molecular geometry.
- 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.