The chemical state of a chemical element is its electronic, chemical and physical nature as it exists in combination with a group of one or more other elements or in its natural "elemental state. Material scientists, solid state physicists, analytical chemists, surface scientists and spectroscopists describe or characterize the chemical, physical and/or electronic nature of the surface or the bulk regions of a material as having or existing as one or more chemical states.
The chemical state set comprises and encompasses these subordinate groups and entities: chemical species, functional group, anion, cation, oxidation state, chemical compound and elemental forms of an element.
This term or phrase is commonly used when interpreting data from analytical techniques such as:
A chemical state can exist on or inside the surface of a solid state material and can often, but not always, be isolated or separated from the other chemical species found on the surface of that material. Surface scientists, spectroscopists, chemical analysts, and material scientists frequently describe the chemical nature of the chemical species, functional group, anion, or cation detected on the surface and near the surface of a solid state material as its chemical state.
To understand how a chemical state differs from an oxidation state, anion, or cation, we compare sodium fluoride (NaF) to poly-tetrafluoro-ethylene (PTFE, Teflon TM). Both contain fluorine, the most electronegative element, but only NaF dissolves in water to form separate ions, Na+ and F-. The electronegativity of the fluorine strongly polarizes the electron density that exists between the carbon, C, and the fluorine, F, but not enough to produce ions which would allow it to dissolve in the water. The carbon and fluorine in Teflon (PTFE) both have a zero (0) electronic charge since they form a covalent bond, but few scientists describe those elements as has having a zero (0) oxidation state. On the other hand, many elements, in their pure form, are often described as existing with a zero oxidation state. This is one of those quirks of nomenclature that have survived over the years.
The chemical state of an element is often confused with its oxidation state. The chemical state of an element or a group of elements that has a non-zero ionic charge, eg (1+), (2+), (3+), (1-), (2-) (3-), is defined as the oxidation state of that element or group of elements. Elements or chemical groups that have an ionic charge can usually be dissolved to form ions in either water or another polar solvent. Such a compound or salt is described as an ionic compound with ionic bonds which means that, in effect, all of the electron density of one or more valence electrons has been transferred from the less electronegative group of elements to the more electronegative group of elements. In the case of a non-ionic compound the chemical bonds are non-ionic such that the compound will probably not dissolve in water or another polar solvent. Many non-ionic compounds have chemical bonds that share the electron density that binds them together. This type of chemical bond is either a non-polar covalent bond or a polar covalent bond.
A functional group is very similar to a chemical species and a chemical group. A chemical group or chemical species exhibits a distinctive reaction behavior or a distinctive spectral signal when analyzed by various spectroscopic methods. These three groupings are often used to describe the groups of elements that exist within an organic molecule.