Crystal field theory explains the energetic properties of transition metal compounds, including color and texture, but cannot describe their bonds. Developed in the 1930s, it was combined with ligand field theory to better understand bonding. The theory describes the interaction between metal and non-metal atoms, and the stable energy fields they generate. It is particularly good at describing coloration, as the range of electron movement determines the absorbed and reflected wavelengths of light.
Crystal field theory describes the electrical activity between the atoms of a transition metal compound. With a focus on the electrical activity between the atoms in these compounds, this theory serves to explain the energetic properties of a transition metal compound, including its color, texture, and magnetic field. Although the atoms within these compounds are bonded to each other, crystal field theory cannot be used to describe these bonds. Incomplete by itself, this theory has been combined with ligand field theory to help understand the bonding between atoms.
In the 1930s, crystalline field theory was developed by physicists John Hasbrouck van Vleck and Hans Bleke. These scientists developed their theory together with, though separate from, ligand field theory. Soon after the development of these two theories, other scientists combined the principles of the two, both of which are now studied with modern ligand field theory. Combining these two theories created a system of equations that was able to better describe the energy fields and molecular bonds within some types of compounds.
Transition metal compounds can be partially described using crystal field theory. These compounds consist of atoms of a particular metal that are surrounded by non-metal atoms, called ligands in this context. The electrons of these different atoms interact in ways that can be described using crystal field theory. The bonds that arise from these electron interactions are also described using ligand field theory.
The term crystalline field, in crystalline field theory, comes from the electric field generated by a group of ligands. These atoms generate a stable energy field within which a transition metal is trapped. These fields can have a variety of different geometric shapes. Many transition metal compounds have cube-shaped fields because such fields are particularly stable and can resist the influence of atoms that are not in the system so that the transition metal compound remains more stable.
One thing crystal field theory is particularly good at describing is the coloration of a transition metal compound. Being a relatively stable structure, the electrons in a particular type of compound approach or move away from their nuclei within a limited range. This range determines the color of the substance because it absorbs certain wavelengths of light that correspond to the distance the electron travels when it is excited. The absorbed wavelengths are not visible in this compound. Instead, the opposite color, as seen on the color wheel, is reflected back, giving the substance its visible color.
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