Transferring Electrons with Redox Reactions

Redox reactions — reactions in which there’s a simultaneous transfer of electrons from one chemical species (chemical entity such as an atom or molecule) to another — are really composed of two different reactions:

✓ Oxidation: A loss of electrons

✓ Reduction: A gain of electrons

These reactions are coupled, because the electrons that are lost in the oxidation reaction are the same electrons that are gained in the reduction reaction. In fact, these two reactions (reduction and oxidation) are commonly called half-reactions, because you need these two halves to make a whole reaction, and the overall reaction is called a redox (reduction/oxidation) reaction. The zinc metal loses electrons and the copper II ion gains them.