oxidation

Oxidation is a chemical process characterized by an increase in the oxidation state of atoms within a substance, typically by loss of electrons. The term originated from reactions with oxygen, historically described as substances 'oxidizing' when they combined with oxygen. In modern chemistry, oxidation is defined more generally as electron loss, and oxidation states provide a bookkeeping method for tracking electrons during reactions.

In redox chemistry, oxidation is always coupled to reduction: one substance loses electrons while another gains them. Substances that gain electrons are oxidizing agents; those that donate electrons are reducing agents.

Oxidation states can change by increments of one or more. Commonly, metals increase oxidation state during corrosion, e.g., iron metal (Fe0) becoming iron(III) oxide (Fe3+ in oxide). Oxygen atoms often increase oxidation number when forming oxides, while hydrogen is often oxidized to H+. Organic oxidation often proceeds from alcohols to aldehydes or carboxylic acids through intermediate steps.

Practically, oxidation occurs in many contexts: rusting of iron, combustion of fuels, synthesis of fine chemicals via selective oxidation, and in metabolism where organisms oxidize nutrients to release energy. Oxidation reactions are facilitated by oxidizing agents such as molecular oxygen, hydrogen peroxide, permanganate, and dichromate, and are often accelerated by catalysts.

In biology and energy storage, oxidation is central to cellular respiration and to redox reactions in batteries and fuel cells. Redox potential, expressed as standard electrode potential, helps predict reaction direction and feasibility.

Safety and environmental considerations arise because strong oxidizers can promote rapid and exothermic reactions. Understanding oxidation is essential across chemistry, physics, biology, and environmental science.