 |
The following list contains terms and concepts that are associated with molecular geometry. |
|
|
|
| |
The following list contains terms and concepts that are associated with molecular geometry. |
|
|
|
|
The Axial Position is a specific location on structures that have expanded octets. Because of the geometric needs of five and six group structures, these systems have two positions for external atoms that are aligned at 1800 to each other. The name of the position is derived from the idea that the structure can rotate on a line drawn through these positions, or they serve as an axis of rotation.  |
|
A Bent Molecule is a structure that consists of three atoms bonded so that one of the three serves as the vertex of an angle made by the three atoms. The angle formed will be non-linear, less than 1800. Bent structures will usually produce polar molecules if the bonded atoms have different electronegativity values.  |
| A Bond Angle is the angle that is formed between three atoms with one of the atoms located at the vertex of the angle. Bond angles are usually measured in the order external atom, central atom, external atom. |
|
A dipole is a combination of partial positive charge and a partial negative charge located within a single structure. If the two charged areas are located at opposite ends of a bond, then the bond has a dipole. If the two charged areas exist as net charges within a molecule, then the molecule has a dipole. When a net dipole exists in a molecule, the molecule is said to be polar. Dipoles introduce certain characteristics into structures that are based on their abilities to react to other areas of charge in the environment. Dipoles exist is systems that consist of two atoms with different electronegativity values being bonded to each other.  |
|
The Equatorial Positions are designations for locations of atoms on geometric shapes that occur in expanded octet structures. Specifically, these structures have a series of locations that approximate the position of the equator on the Earth. They are positions that exist 900off of the axis of rotation for these structures. |
| The concept of the Expanded Octet occurs in any system that has an atom with more than four electron pairs attached to it. Most commonly, atoms will expand their octets to contain a total of five or six electron pairs, in total. In theory, it is possible to expand beyond those number. The large amounts of negative charge concentrated in small volumes of space prevent those larger expanded octets from forming. When an atom expands its octet, it does so by making use of empty d orbitals that are available in the valence level of the atom doing the expanding. Atoms that do not have empty valence level d orbitals will not be able to expand their octets. The atom that expands its octet in a structure will usually be located in the center of the structure and the system will not use any multiple bonds in attaching atoms to the central atom. The process of expanding octets is strictly a last resort on the part of atoms. |
| Lewis Dot Structures, or electron dot structures, are schematic pictures of molecules. They are used primarily to show the types of bonding employed in the system and the assignment of nonbonded electron pairs. These structures can be interpreted to give information about the molecular geometry of a system. |
Linear Geometry
Linear Geometry is an arrangement of three atoms that places them at an angle of 1800, where the vertex of the angle is the second atom in the sequence.
|
Molecular Geometry is the overall arrangement of the atoms in a molecule. As the numbers of atoms in molecules increases, the concept of molecular geometry is rendered meaningless because of the complexity of the system. The bonded atoms in a molecule are responsible for determining the molecular geometry of a system. Nonbonded electron pairs are not considered in determining molecular geometry. For instance, this structure is based on a central atom that has a trigonal planar shape, yet the molecule is described as being bent. Notice that the nonbonded electron pair at the top of the structure is disregarded in determining the molecule.  |
| Multiple Bonds are the bonds described as double and triple bonds. They are characterized by consisting of the required sigma bond to hold the structure together, and the extra bonds will be pi bonds that are used to fulfil the octet requirements of the atoms. |
|
Nonbonded Electron Pairs, or unshared electron pairs, are valence electrons that exist on a molecules in locations where the electrons are not involved in the bonding process. Among other things, the nonbonded electron pairs frequently act as locations for future attachment of other structures if the system goes through a reaction.  |
|
|
kdrews@bcpl.net |  |