Cations

A cation is a positively charged ion formed when an atom or molecule loses one or more electrons. Cations are attracted to the cathode in electrochemical cells and combine with anions to form salts. They can also arise from protonation, as in the formation of ammonium (NH4+) from ammonia, or hydronium (H3O+) in acidic aqueous solutions.

Most cations originate from metals that undergo oxidation, with the charge corresponding to the number of electrons lost. Common inorganic cations include sodium (Na+), potassium (K+), calcium (Ca2+), magnesium (Mg2+), iron (Fe3+), and aluminum (Al3+). Some nonmetals form cations under certain conditions; for example, ammonium (NH4+) forms when ammonia gains a proton.

In solution, cations are typically hydrated, surrounded by water molecules that stabilize the charge. The size and charge of a cation influence its hydration energy, mobility, and the strength of its interactions with anions and ligands. Multivalent cations (such as Ca2+ or Fe3+) generally exhibit higher charge density, stronger hydration, and greater tendency to form complex ions or coordinate with ligands in coordination chemistry.

Cations play essential roles across chemistry, physics, and biology. They participate in the formation of salts, drive electrochemical reactions, and participate in catalysis and materials processing. In biological systems, cation gradients and signaling (for example, Na+, K+, and Ca2+ in cellular processes) are fundamental to function.