Chemical Reactions - Redox reactions

Oxidation is defined as the loss of electrons, the gain of oxygen, or the loss of hydrogen. It leads to an increase in the oxidation state of an element (e.g., $Mg \rightarrow Mg^{2+} + 2e^-$).

Reduction is defined as the gain of electrons, the loss of oxygen, or the gain of hydrogen. It leads to a decrease in the oxidation state of an element (e.g., $Cl_2 + 2e^- \rightarrow 2Cl^-$).

A Redox reaction is a chemical process in which both oxidation and reduction occur simultaneously. The mnemonic OIL RIG (Oxidation Is Loss, Reduction Is Gain) helps remember electron transfer.

Oxidizing Agents (oxidants) are substances that accept electrons from other species. In the process, the oxidizing agent is itself reduced.

Reducing Agents (reductants) are substances that donate electrons to other species. In the process, the reducing agent is itself oxidized.

Oxidation Number (or State) is a value assigned to an atom to represent the number of electrons lost or gained. Rules include: elements in their native state are $0$, oxygen is usually $-2$, and hydrogen is usually $+1$.

The sum of oxidation numbers in a neutral compound is $0$. In a polyatomic ion, the sum equals the charge of the ion (e.g., in $SO_4^{2-}$, the sum is $-2$).

Disproportionation is a specific type of redox reaction where the same element is simultaneously oxidized and reduced from a single oxidation state to two different states.