Al3

Al3 is not a single, universally defined term in chemistry. Its meaning depends on context and discipline. In inorganic chemistry, Al3 or Al3+ denotes aluminum in the +3 oxidation state, which is the most stable form of aluminum in aqueous solutions and most compounds. In solution, Al3+ is highly reactive and undergoes hydrolysis, forming species such as Al(OH)2+, Al(OH)2+, and ultimately Al(OH)3 as pH rises; complex formation with ligands such as fluoride or organic molecules modulates solubility and speciation. Aluminum(III) complexes are common in coordination chemistry, mineralogy, and environmental science, and the behavior of Al3+ in water treatment and soil chemistry is of practical importance.

In a different use, Al3 may refer to a neutral triatomic aluminum cluster, a small molecule consisting of three aluminum atoms studied in cluster chemistry and spectroscopy. Such clusters are typically generated in gas-phase experiments (for example, by laser ablation) and analyzed with mass spectrometry and electronic-structure calculations. The geometry and electronic structure of Al3 are subjects of theoretical and experimental study, reflecting how metallic bonding and bonding patterns evolve from individual atoms to larger aluminum clusters and to bulk metal. Because Al3 is highly reactive and short-lived, its characterization relies on rapid, controlled experimental conditions and sophisticated computational methods.