An oxidation number is a number assigned to anelement in chemical combination that represents the number of electrons lost (or gained, if the number is negative), by an atom of that element in the compound.
The termredox comes from the two concepts ofreduction andoxidation. It can be explained in simple terms:
Reduction describes thegain of electrons by a molecule, atom or ion
Whether an electron is gained or lost can be easily memorised by the abbreviation OIL RIG, which stands for, "Oxidation Is Loss," or losing electrons, and "Reduction Is Gain," or gaining electrons. Redox reactions can also happen by sharing electrons to form a product bycovalent bonding. The term is called redox as neither oxidation or reduction may occur without the other occuring.[2]
In an oxidation reduction reaction, the cation gives an electron to the anion because both ions will have a different charge to attract each other with. In an oxidation reduction reaction, the oxidizingreagent pulls an electron from the other atom to have a net positive charge. The reducing reagent gives an electron to have a net negative charge. However, there are exceptions.[3]
Redox is a chemical process. It can be described inchemical formulas. This example describes the process that occurs in ablast furnace, whereiron (Fe) reacts with carbon (C):
↑This can be a simple redox process, such as theoxidation ofcarbon to yieldcarbon dioxide, the reduction of carbon byhydrogen to yieldmethane (CH4), or a complex process such as the oxidation of sugar in the human body, through a series of very complexelectron transfer processes.
↑Oxidation and reduction properly refer toa change in oxidation number – the actual transfer of electrons may never occur. Thus, oxidation is better defined as anincrease in oxidation number, and reduction as adecrease in oxidation number. In practice, the transfer ofelectrons will always cause a change in oxidation number, but there are many reactions which are classed as "redox" even though no electron transfer occurs (such as those involvingcovalent bonds).
