Redox
Redox (short for reduction–oxidation) reactions are chemical reactions in which electrons are transferred from one substance to another. Oxidation is the loss of one or more electrons, and reduction is the gain of one or more electrons.[1] Redox reactions differ from acid–base reactions, which transfer protons rather than electrons.[1]
Changing meanings
The word oxidation originally meant combining with oxygen. Its meaning was later widened to combining with other electronegative elements, and it now means the removal of electrons. Reduction is the gain of electrons.[2] The term "redox" is recommended because it emphasises that such reactions are reversible.[2]
An example
When zinc metal is placed in a solution containing copper ions, the reaction is:
- Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)
Zinc loses electrons, so it is oxidised; it is called the reducing agent. The copper ions gain electrons, so they are reduced; they are the oxidising agent.[1]
The reaction can be split into two half-reactions, which show only the substance being oxidised or reduced together with the electrons lost or gained:[3]
- Zn → Zn2+ + 2e−
- Cu2+ + 2e− → Cu
Added together, these give the overall equation.[3]
Oxidising and reducing agents
The halogens and oxygen are good oxidising agents. The alkali metals, the alkaline earth metals and aluminium are excellent reducing agents, while the coinage metals (copper, silver and gold) are poor reducing agents.[3] The strength of an oxidising or reducing agent can be measured as a redox potential, compared with a standard hydrogen electrode, which is given a value of 0.000 volts at 25 °C.[2]
Oxidation numbers
An oxidation number (or oxidation state) is the number of electrons an atom has gained (shown as negative) or lost (shown as positive) compared with the neutral atom. It is not always the actual charge on the atom.[3] Some simple rules are used to assign them: atoms in a pure element have an oxidation number of 0, a monatomic ion has an oxidation number equal to its charge, and oxygen is usually −2.[4] Oxidation numbers are especially useful for covalent substances, where the transfer of electrons is less obvious, such as in the reaction of hydrogen with chlorine to form hydrogen chloride.[2]
Discovery of noble gas compounds
In 1962 the chemist Neil Bartlett used platinum hexafluoride, a very powerful oxidising agent, to make the first compound of the noble gas xenon. He had noticed that xenon and oxygen need almost the same energy to remove an electron.[5]
See also
References
- ↑ 1.0 1.1 1.2 Young, Susan M.; Vining, William J.; Day, Roberta; Botch, Beatrice (2018). General Chemistry: Atoms First. Boston: Cengage Learning. p. 246. ISBN 978-1-337-61229-6.
{{cite book}}:|access-date=requires|url=(help) - ↑ 2.0 2.1 2.2 2.3 Mackay, K. M.; Mackay, R. A.; Henderson, W. (2002). Introduction to Modern Inorganic Chemistry (6th ed.). Cheltenham: Nelson Thornes. section 6.3: Oxidation and reduction. ISBN 0-7487-6420-8. Retrieved 2026-10-23.
- ↑ 3.0 3.1 3.2 3.3 Young, Susan M.; Vining, William J.; Day, Roberta; Botch, Beatrice (2018). General Chemistry: Atoms First. Boston: Cengage Learning. p. 247. ISBN 978-1-337-61229-6.
{{cite book}}:|access-date=requires|url=(help) - ↑ Young, Susan M.; Vining, William J.; Day, Roberta; Botch, Beatrice (2018). General Chemistry: Atoms First. Boston: Cengage Learning. p. 248. ISBN 978-1-337-61229-6.
{{cite book}}:|access-date=requires|url=(help) - ↑ Brock, William H. (1992). The Fontana History of Chemistry (ePub ed.). London: Fontana Press. Chapter 9: Principles of Chemistry, section The Inert Gases. ISBN 9780007394968.
{{cite book}}:|access-date=requires|url=(help)