Chlorine

Actinium chloride

A white, hygroscopic salt used in some of the earliest experiments to pin down actinium's properties, prepared and handled only in trace amounts because natural actinium is so scarce.

Used for: Used in early radiochemical studies establishing actinium's atomic weight

Aluminum chloride

A covalent compound in its anhydrous form and a strong Lewis acid, often existing as the dimer Al2Cl6 in the vapor phase.

Used for: Catalyst in Friedel-Crafts reactions, antiperspirant active ingredient

Antimony pentachloride

A yellow, fuming liquid and powerful Lewis acid that hydrolyzes readily in moist air, used to catalyze chlorination reactions.

Used for: Catalyst for chlorination and polymerization reactions

Antimony trichloride

A white, fuming solid known historically as "butter of antimony," used as a chlorinating agent and Lewis acid catalyst in organic synthesis.

Used for: Catalyst and intermediate in organic and dye chemistry

Barium chloride

A water-soluble, toxic barium salt used in analytical chemistry to test for sulfate ions, which precipitate out as insoluble barium sulfate.

Used for: Laboratory reagent for sulfate testing and metal heat treatment

Beryllium chloride

A covalent chloride that forms polymer-like chains in the solid state rather than a simple ionic lattice, reflecting beryllium's small size and high charge density.

Used for: Industrial intermediate for producing metallic beryllium

Bismuth oxychloride

A pearly white powder built from stacked layers that scatter light with a soft, nacre-like shimmer, giving it an optical effect similar to ground mother-of-pearl.

Used for: Pearlescent shimmer pigment in cosmetics such as eyeshadow and foundation

Bismuth trichloride

A moisture-sensitive white solid that fumes in humid air as it hydrolyzes, and acts as a comparatively gentle, low-toxicity Lewis acid in organic chemistry.

Used for: Lewis acid catalyst in organic synthesis

Cadmium chloride

A white, water-soluble salt used mainly as a laboratory and industrial source of dissolved cadmium ions. It forms a distinctive layered crystal structure that is often cited as a reference lattice in chemistry.

Used for: Precursor for depositing cadmium sulfide and cadmium telluride films

Calcium chloride

A highly water-soluble ionic salt that releases heat as it dissolves and readily pulls moisture from the air. It forms colorless, brittle crystals when dry.

Used for: De-icing roads and sidewalks, food preservative, drying agent

Californium trichloride

A green crystalline solid and one of the best-characterized californium compounds, made by reacting californium oxide with anhydrous hydrogen chloride. It reflects californium's dominant +3 oxidation state in the solid state.

Cerium(III) chloride

A white, hygroscopic salt that is the standard entry point into cerium(III) chemistry and a mild Lewis acid used to tame reactive organometallic reagents.

Used for: Lewis acid additive in organic synthesis (Luche reduction)

Cesium chloride

A simple ionic salt whose crystal structure gives its name to a common packing arrangement, and whose dense solutions are used to separate biomolecules by density.

Used for: Density-gradient medium for separating DNA and other biomolecules

Chloroauric acid

A yellow-orange, highly water-soluble acid formed when gold dissolves in aqua regia, serving as the standard source of dissolved gold for chemical and electrochemical work.

Used for: Starting material for gold electroplating and nanoparticle synthesis

Chloroform

A dense, sweet-smelling liquid in which three of methane's hydrogens are replaced by chlorine atoms. It was historically used as a surgical anesthetic before its toxicity was well understood.

Used for: Industrial solvent and precursor in refrigerant manufacturing

Chloroplatinic acid

A reddish-brown, highly water-soluble acid containing the hexachloroplatinate anion, typically handled as a hydrate and used as the entry point into most platinum chemistry.

Used for: Catalyst precursor in silicone curing and metal plating

Chromium(III) chloride

A solid that appears violet when anhydrous but shifts toward green as it picks up water, a striking demonstration of how coordinated water molecules change a transition metal ion's color.

Used for: Precursor for chromium catalysts and mordant in textile dyeing

Cisplatin

A square-planar platinum(II) complex bearing two ammonia and two chloride ligands arranged on the same side of the molecule, a geometry that is essential to how it binds and disrupts DNA.

Used for: Widely used chemotherapy drug for treating various cancers

Cobalt(II) chloride

A salt famous for its reversible color change with humidity — deep blue when anhydrous and pink when hydrated — which makes it a classic visual indicator of moisture in the air.

Used for: Humidity indicator in silica gel packets and desiccants

Copper(II) chloride

A yellow-brown solid (green when hydrated) well known for imparting a distinctive blue-green color to flames, a property used in flame tests and pyrotechnics alike.

Used for: Flame-coloring agent in pyrotechnics and catalyst in organic synthesis

Dysprosium(III) chloride

A pale yellow-green, hygroscopic dysprosium salt normally handled as its hexahydrate, serving as the common entry point into dysprosium chemistry.

Used for: Laboratory precursor for dysprosium metal and other dysprosium compounds

Erbium(III) chloride

A violet-pink, hygroscopic erbium salt handled in the laboratory as its hydrate, serving as a common precursor for other erbium compounds.

Used for: Precursor for erbium-doped optical fiber amplifier glass

Europium(II) chloride

One of the few lanthanide dihalides that is genuinely stable, reflecting europium's unusually accessible +2 oxidation state and its chemical resemblance to the alkaline-earth metals.

Used for: Research reagent for europium(II) luminescent materials

Europium(III) chloride

A pale yellow, water-soluble europium salt in which europium holds its common +3 state, typically handled in the laboratory as its hydrate.

Used for: Laboratory precursor for europium luminescent and coordination compounds

Gadolinium(III) chloride

A white, deliquescent gadolinium salt used throughout gadolinium chemistry as the entry point for making other gadolinium compounds, including its highly paramagnetic complexes.

Used for: Laboratory precursor for gadolinium coordination and contrast-agent chemistry

Germanium tetrachloride

A colorless, fuming liquid that hydrolyzes readily in moist air to form germanium dioxide and hydrochloric acid. It serves as the key industrial precursor for high-purity germanium compounds.

Used for: Precursor for germanium-doped optical fiber cores

Gold(I) chloride

A yellow, light-sensitive solid with gold in its +1 state, forming zigzag chains of linearly coordinated gold atoms that readily disproportionate into gold metal and gold(III) chloride.

Used for: Catalyst in organic synthesis, particularly alkyne activation

Gold(III) chloride

A red, dimeric solid in which each square-planar gold(III) center acts as a strong Lewis acid, readily hydrolyzing when exposed to water.

Used for: Catalyst in organic synthesis and precursor for gold nanoparticles

Hafnium tetrachloride

A white, moisture-sensitive solid that fumes in air as it hydrolyzes, serving as the key precursor for depositing hafnium compounds by vapor-phase processes.

Used for: Precursor gas for depositing hafnium dioxide gate dielectrics

Holmium(III) chloride

A bright yellow, hygroscopic holmium salt typically handled as its hydrate, used as a common laboratory starting material for other holmium compounds.

Used for: Precursor for holmium metal and holmium-doped laser crystals

Hydrochloric acid

A strong acid formed by dissolving hydrogen chloride gas in water, which fully ionizes into H⁺ and Cl⁻ ions in solution. It's also the main component of gastric acid in the human stomach.

Used for: Industrial metal cleaning (pickling), food processing, digestion in the stomach

Indium(III) chloride

A white, highly hygroscopic solid that acts as a mild Lewis acid catalyst and serves as the usual starting point for making other indium compounds.

Used for: Lewis acid catalyst in organic synthesis

Iridium(III) chloride

A dark green to black crystalline solid with iridium in its +3 oxidation state. The anhydrous form is chemically inert and barely soluble, while the hydrated form dissolves readily in water.

Used for: Starting material for synthesizing other iridium catalysts and complexes

Lanthanum(III) chloride

A white, hygroscopic salt that serves as the standard water-soluble entry point into lanthanum chemistry.

Used for: Laboratory precursor for lanthanum compounds and catalysts

Lead(II) chloride

A white, sparingly soluble solid that forms an orthorhombic crystal structure known as cotunnite, and serves as a common intermediate when converting lead ores into other lead compounds.

Used for: Intermediate in lead refining and manufacture of other lead salts

Lithium chloride

A highly hygroscopic ionic salt that pulls moisture from the air so effectively it is used as a drying agent, releasing noticeable heat as it dissolves.

Used for: Desiccant and dehumidifier, brazing flux for aluminum

Lutetium(III) chloride

A white, hygroscopic lutetium salt handled in the laboratory as its hydrate, serving as a common precursor for other lutetium compounds.

Used for: Laboratory precursor for lutetium metal and lutetium compounds

Magnesium chloride

A highly soluble ionic salt that readily absorbs moisture from air, and one of the major dissolved salts extracted from seawater.

Used for: Road de-icing, tofu coagulant (nigari), magnesium metal production

Mercury(I) chloride

Known as calomel, a nearly insoluble white solid built around a metal-metal bonded Hg2²⁺ ion rather than separate Hg⁺ centers, which is unusual for a group 12 element.

Used for: Reference electrode component in electrochemistry (calomel electrode)

Mercury(II) chloride

A white crystalline solid once known as corrosive sublimate, notable for dissolving as largely undissociated molecules rather than free ions despite being an ionic-looking salt.

Used for: Historic wood preservative and disinfectant, now largely discontinued for its toxicity

Neodymium(III) chloride

A mauve, hygroscopic salt that serves as the standard water-soluble starting material for neodymium chemistry.

Used for: Laboratory precursor for neodymium compounds and catalysts

Nickel(II) chloride

A yellow-brown solid that turns green upon hydration, serving as a common, water-soluble entry point for preparing other nickel compounds and catalysts.

Used for: Catalyst precursor in organic synthesis and nickel electroplating

Niobium pentachloride

A yellow, moisture-sensitive solid that is the standard entry point into niobium chemistry, readily converted into other niobium compounds.

Used for: Precursor for niobium catalysts and organoniobium compounds

Osmium(III) chloride

A dark brown to black, water-insoluble solid commonly used as the starting point for making other osmium compounds and complexes.

Used for: Laboratory precursor for osmium coordination chemistry and catalysts

Palladium(II) chloride

A brownish-red salt and the most important commercial palladium compound, serving as the entry point for the vast majority of palladium catalysts used in industry.

Used for: Precursor for palladium cross-coupling catalysts and carbon monoxide detectors

Platinum(II) chloride

An olive-green to brown, water-insoluble solid built from square-planar platinum(II) centers, occurring in polymeric chain or cluster forms depending on how it is prepared.

Used for: Precursor for platinum catalysts used in hydrosilylation reactions

Platinum(IV) chloride

A reddish-brown solid with platinum in its +4 oxidation state, made by chlorinating platinum metal at high temperature and used as a gateway to many other platinum compounds.

Used for: Precursor for chloroplatinic acid and other platinum complexes

Polonium tetrachloride

A bright yellow, water-soluble solid and the best-characterized of polonium's halides, prepared and studied only ever in microgram quantities because of polonium's intense radioactivity.

Used for: Used in tracer-scale studies of polonium's chemical behavior

Polyvinyl chloride

A synthetic polymer built from repeating vinyl chloride units, valued for being durable, lightweight, and resistant to weathering. It's one of the most widely produced plastics in the world.

Used for: Plumbing pipes, window frames, cable insulation, flooring

Potassium chloride

An ionic salt closely related to table salt, forming colorless cubic crystals that dissolve readily in water. It occurs naturally as the mineral sylvite.

Used for: Potassium fertilizer, salt substitute, and IV saline solutions

Praseodymium(III) chloride

A light green, hygroscopic salt that provides the standard water-soluble route into praseodymium chemistry.

Used for: Laboratory precursor for praseodymium compounds

Protactinium pentachloride

A pale yellow solid built from chains of chlorine-bridged protactinium atoms, notable for subliming readily under vacuum rather than melting cleanly.

Used for: Precursor used in the reduction of protactinium to its metallic form

Radium chloride

A white salt that was the first radium compound ever isolated in pure form, by Marie and Pierre Curie in 1898, and one that visibly glows faintly in the dark from its own intense radioactivity.

Used for: Historic first isolated radium compound, later used in early radiotherapy sources

Rhodium(III) chloride

A dark red salt that is the principal commercial entry point for producing rhodium catalysts and other rhodium compounds.

Used for: Precursor for industrial rhodium catalysts, including Wilkinson's catalyst

Rubidium chloride

A simple white ionic salt and the most common laboratory source of rubidium, used as a biological tracer because it behaves like potassium in living cells.

Used for: Cell-biology tracer for potassium transport; ceramic glazes

Ruthenium(III) chloride

A dark, water-soluble salt that is the most common commercial starting material for ruthenium chemistry, used to make countless ruthenium catalysts and complexes.

Used for: Precursor for homogeneous catalysts, including ruthenium olefin metathesis catalysts

Samarium(III) chloride

An ionic samarium(III) salt that forms hygroscopic hydrated crystals in air and is the usual starting point for making other samarium compounds.

Used for: Precursor for synthesizing organosamarium and catalytic samarium compounds

Silver chloride

An almost completely insoluble white silver salt that darkens rapidly under light as it breaks down into metallic silver. That light sensitivity made it central to early photographic chemistry.

Used for: Light-sensitive coating in traditional photographic film

Sodium chloride

Ordinary table salt — an ionic lattice of Na⁺ and Cl⁻ ions in a simple cubic arrangement. It's the most abundant dissolved salt in seawater and the main mineral in rock salt deposits.

Used for: Food seasoning and preservation, de-icing roads, industrial chlor-alkali production

Sodium hypochlorite

The sodium salt of hypochlorous acid, sold as a pale yellow-green aqueous solution. It's a strong oxidizer that breaks down pigments and destroys microorganisms.

Used for: Active ingredient in household bleach and water disinfection

Strontium chloride

A white, water-soluble salt of strontium that colors flames a vivid red, a property put to use in fireworks and signal flares.

Used for: Toothpaste ingredient for sensitive teeth; red colorant in fireworks

Tantalum pentachloride

A pale yellow, moisture-sensitive solid that fumes in humid air, used as the principal starting material for making other tantalum compounds.

Used for: Precursor for high-purity tantalum metal and tantalum oxide films

Terbium(III) chloride

A white to pale-tan, hygroscopic terbium salt used as a common laboratory starting material for other terbium(III) compounds.

Used for: Precursor for synthesizing terbium phosphor and magnetic compounds

Tetraamminepalladium(II) chloride

A water-soluble coordination compound in which four ammonia molecules surround a central palladium ion, used as a convenient palladium source for plating baths.

Used for: Palladium source in electroless and electrolytic plating solutions

Thallium(I) chloride

A white, light-sensitive solid whose low solubility and crystal structure closely parallel silver chloride, a reflection of how similarly thallium(I) and silver(I) ions behave in solution.

Used for: Laboratory reagent for preparing other thallium compounds

Thorium tetrachloride

A white, strongly hygroscopic solid that fumes on contact with moist air, serving as a common laboratory starting point for making other thorium compounds.

Used for: Laboratory precursor for synthesizing other thorium compounds

Thulium(III) chloride

A yellow, hygroscopic thulium salt normally handled as its hydrate, used as a common laboratory starting material for other thulium compounds.

Used for: Laboratory precursor for thulium metal and thulium compounds

Tin(II) chloride

A white crystalline reducing agent, also called stannous chloride, that readily oxidizes to tin(IV) when exposed to air or moisture.

Used for: Reducing agent in chemical analysis and tin-based mirror silvering

Tin(IV) chloride

A colorless, fuming liquid, also known as stannic chloride, that reacts vigorously with water and was once used as a smoke-screen agent.

Used for: Catalyst in organic synthesis and precursor for tin oxide coatings

Vanadium(III) chloride

A violet, moisture-sensitive solid that serves as a common laboratory entry point into vanadium chemistry, since it can be readily converted into a wide range of other vanadium(III) compounds.

Used for: Precursor for vanadium catalysts used in olefin polymerization

Wilkinson's catalyst

A landmark rhodium complex bearing three triphenylphosphine ligands that catalyzes the hydrogenation of alkenes under mild conditions, a discovery that helped found modern homogeneous catalysis.

Used for: Homogeneous catalyst for hydrogenating alkenes in organic synthesis

Ytterbium(III) chloride

A white, hygroscopic ytterbium salt typically handled as its hydrate, used as a common laboratory starting material for other ytterbium compounds.

Used for: Precursor for ytterbium metal and ytterbium-doped optical materials

Yttrium chloride

A white, hygroscopic salt that serves as a common laboratory starting point for making other yttrium compounds and yttrium metal.

Used for: Precursor for yttrium metal production and organoyttrium chemistry

Zinc chloride

A white, extremely water-absorbing solid that dissolves readily and acts as an effective flux, helping molten metal wet and bond to surfaces during joining processes.

Used for: Flux in soldering and galvanizing; wood preservative

Zirconium tetrachloride

A white, moisture-sensitive solid that fumes in air and serves as the key intermediate in refining zirconium metal from its ores.

Used for: Intermediate in zirconium metal purification and a catalyst component