Aluminum chloride is a chemical compound found in various industrial and laboratory settings. It is widely used in chemical reactions as a powerful acid and plays a role in the manufacturing of many products. Its applications range from complex organic synthesis to common household items.
Identifying the Formula
The chemical formula for aluminum chloride is AlCl3. This formula indicates the precise elemental composition of the compound in its most common form. It is created from the reaction between aluminum metal and chlorine gas. The formula shows that one atom of aluminum (Al) combines with three atoms of chlorine (Cl) to form a single, electrically neutral unit.
The compound is also referred to by its systematic name, aluminum trichloride, which reflects the presence of the three chlorine atoms. The anhydrous form, meaning without water, is the pure compound represented by this formula.
Understanding the Bonding Structure
The formula AlCl3 results from how aluminum and chlorine atoms achieve electrical neutrality. Aluminum (Al) is a metal that readily loses three electrons, forming a positively charged ion, Al3+. Chlorine (Cl) is a nonmetal that needs one electron to complete its outer shell, forming a negatively charged ion, Cl-.
For the compound to have a neutral charge, the +3 charge of the aluminum ion must be balanced by the negative charges of the chloride ions. This balance requires three chloride ions, each with a -1 charge, to combine with one aluminum ion (Al3+ + 3Cl- → AlCl3). Although the anhydrous solid has covalent characteristics and exists as a dimer (Al2Cl6) in the gas phase, the simple AlCl3 formula represents the 1:3 ratio of atoms and the overall charge balance.
Key Physical Characteristics
Anhydrous aluminum chloride presents as a white, crystalline solid at room temperature. Samples often appear light yellow due to trace contamination, most commonly from iron(III) chloride. The compound exhibits a melting point of approximately 192°C.
It sublimes at around 180°C, transitioning directly from a solid to a gas without passing through a liquid state at atmospheric pressure. Aluminum chloride is highly hygroscopic, readily absorbing moisture from the air. When it encounters water, it reacts aggressively, undergoing hydrolysis to produce heat and fumes of hydrogen chloride.
Common Industrial Uses
Aluminum chloride is valued in industrial chemistry, primarily for its function as a Lewis acid, making it an effective catalyst. Its main use is in organic synthesis, particularly catalyzing the Friedel-Crafts reaction, a method for attaching chemical groups to aromatic rings. These reactions are used in the production of petrochemicals, dyes, and pharmaceuticals.
The compound also plays a part in the commercial production of aluminum metal through the electrolysis of molten salts. Additionally, it is included as an active ingredient in many antiperspirants. In this role, it forms a temporary gel that physically blocks the sweat ducts, reducing the amount of moisture released onto the skin surface.