Chemistry

Ionization energy: definition, periodic trends, causes and significance Ionization energy Ionization energy is the energy needed to remove an electron from an isolated atom or ion. This article explains its definition, successive energies, periodic trends, causes, excep…

Iridium (element 77) Iridium Iridium is a rare, dense transition metal (symbol Ir, atomic number 77) in the platinum group, noted for extreme corrosion resistance, high melting point, and specialized industria…

Iron (Fe, atomic number 26): properties, occurrence, and uses Iron Iron (Fe, atomic number 26): a silvery, magnetic metal — overview of physical and chemical properties, global occurrence from core to ore deposits, major uses in steel and tools, b…

Iron chloride Iron chloride refers to inorganic iron–chlorine salts, chiefly iron(II) chloride (FeCl2) and iron(III) chloride (FeCl3): their properties, hydrates, preparation, uses, chemistry an…

Iron oxides: types, properties, occurrence, uses and cultural significance Iron oxide Overview of iron oxides: common chemical forms (hematite, magnetite, wüstite), colors and magnetic properties, natural occurrence and mining, historical pigment uses, industrial an…

Iron sulfide and related iron–sulfur compounds Iron sulfide Iron sulfide (FeS) is a black inorganic solid of iron(II) and sulfide. This article explains its chemistry, crystal forms, common minerals such as pyrite, reactions with acids, use…

Iron(II,III) oxide (magnetite): properties, structure, uses Iron(II,III) oxide Iron(II,III) oxide (Fe3O4), commonly known as magnetite, is a mixed‑valence iron oxide with magnetic properties, found as a mineral and used in industry, pigments, and magnetic app…

Iron(II) chloride (ferrous chloride) Iron(II) chloride Overview, properties, preparation, uses and safety of iron(II) chloride (ferrous chloride), a common iron salt in the +2 oxidation state used in laboratory and industrial applicati…

Iron(II) hydroxide (Fe(OH)2) — properties, formation, and uses Iron(II) hydroxide Iron(II) hydroxide, Fe(OH)2, is a sparingly soluble ferrous hydroxide that forms a greenish precipitate, oxidizes readily in air, and appears in corrosion, environmental chemistry,…

Iron(II) oxide (FeO): properties, formation, and uses Iron(II) oxide Iron(II) oxide (FeO) is a basic iron oxide that occurs as black wüstite and as hydrated and oxidized forms; it is important in metallurgy, geology, and materials chemistry.

Iron(II) sulfate (ferrous sulfate) Iron(II) sulfate Overview of iron(II) sulfate (FeSO4), its forms and properties, historical uses, modern applications in medicine and industry, and safety and environmental considerations.

Iron(III) chloride (ferric chloride) Iron(III) chloride Iron(III) chloride (FeCl3), known as ferric chloride, is a Lewis-acid inorganic salt used in water treatment, metal etching and organic synthesis; this article summarizes its prope…

Iron(III) nitrate (ferric nitrate) Iron(III) nitrate Inorganic salt Fe(NO3)3, commonly encountered as hydrated ferric nitrate; a water-soluble oxidizing salt used in synthesis, catalysis, dyeing and etching, with characteristic coord…

Iron(III) oxide (Fe2O3): properties, occurrence and uses Iron(III) oxide Iron(III) oxide, Fe2O3, is a common reddish iron oxide found as hematite and rust; it has industrial uses as an ore, pigment and reactant (e.g., thermite) and distinct chemical and…

Iron(III) sulfate (ferric sulfate): properties, uses, and safety Iron(III) sulfate Overview of iron(III) sulfate (Fe2(SO4)3), its composition, properties, common uses in water treatment and industry, preparation, and safety considerations.

Isodesmic reaction A chemical reference reaction in which bond types broken and formed are the same; used in thermochemistry and computational chemistry to compare relative stabilities and reduce sys…

Isolobal principle: relating molecular fragments by frontier orbitals Isolobal principle A qualitative analogy that compares molecular fragments by the similarity of their frontier orbitals (HOMO/LUMO), used to predict bonding, structure and reactivity in organometalli…

Isomer (chemistry): types, properties, and significance Isomer An isomer is one of two or more compounds with the same molecular formula but different arrangements of atoms. This article explains types, examples, historical context, identifica…

Isotope — definition, properties, and uses Isotope An isotope is a form of a chemical element with the same number of protons but a different number of neutrons. Isotopes differ in mass, stability, natural abundance and have many s…

Isotope Electrochemistry Study of how isotopic composition affects and can be manipulated by electrochemical processes; covers separation, kinetic and equilibrium isotope effects, sensors, and applications…

Isotopes of Hydrogen: Protium, Deuterium, Tritium and Beyond Isotopes of hydrogen Summary of hydrogen isotopes — protium, deuterium and tritium — their nuclear properties, natural occurrence, synthetic heavier isotopes, uses in science and industry, and naming c…

Jet fuel: composition, types, history, uses and safety Jet fuel Jet fuel (aviation turbine fuel) is a kerosene-based fuel refined from crude oil for turbine engines. This article covers types, production, properties, uses, history, safety and e…

John Newlands — Law of Octaves and early work on the periodic classification John Newlands English chemist John A. R. Newlands proposed the Law of Octaves, an early arrangement of the chemical elements by atomic weight that revealed repeating properties and helped pave t…

Kerosene (paraffin oil): properties, production, uses, and safety Kerosene Kerosene, also called paraffin oil, is a flammable hydrocarbon fuel distilled from crude oil. This entry covers its composition, production, common uses (lighting, heating, aviatio…

Ketone: structure, properties, and common uses Ketone Ketones are organic compounds with a carbonyl group bonded to two carbon atoms. This article explains their structure, preparation, reactivity, identification by spectroscopy, uses…

Kilojoule per mole (kJ/mol) Kilojoule per mole Energy quantity equal to kilojoules of energy associated with one mole of substance; commonly used in chemistry for reaction enthalpies, free energies and activation energies.

Krypton: a noble gas element (atomic number 36) Krypton Krypton is a colorless, odorless noble gas (Kr, Z=36) used in lighting, lasers and standards. It occurs in trace amounts in air and has a small number of stable isotopes and some r…

Kurt Alder — German chemist and co-discoverer of the Diels–Alder reaction Kurt Alder Kurt Alder (1902–1958), German chemist awarded the 1950 Nobel Prize with Otto Diels for the Diels–Alder cycloaddition; foundational to modern organic synthesis and many industrial…

Laboratory glassware: types, materials, uses, and safety Laboratory glassware Overview of common laboratory glassware, their materials and properties, principal uses in chemistry and biology, brief history, and practical handling and safety considerations.

Laboratory techniques: principles, common methods, and safe practice Laboratory techniques Overview of laboratory techniques: core skills, common procedures, safety practices, historical development, and applications across scientific disciplines.

Lactic acid: properties, production, uses, and biological role Lactic acid Lactic acid is a common organic acid (C3H6O3) produced by fermentation and metabolism. This article covers its chemistry, natural occurrence, industrial production, uses in food an…

Lactose: the milk sugar — chemistry, biology, and uses Lactose Lactose is the disaccharide sugar in mammalian milk. This article explains its chemistry, digestion (lactase), occurrence in dairy, industrial uses, history of the name, and distin…

Lanthanide (lanthanoid) elements: properties, chemistry, uses, and history Lanthanide Lanthanides are the 15 metallic elements with atomic numbers 57–71. They share f‑block electronic structure, a progressive ionic shrinkage called the lanthanide contraction, and im…

Lanthanum: properties, history, occurrence and uses Lanthanum Lanthanum (La, Z=57) is a soft silvery rare-earth metal and the first element of the lanthanide series. It has uses in optics, catalysts, battery alloys and medicine and an importa…

Law of Definite Composition (Law of Definite Proportions) Law of definite composition Principle that a pure chemical compound always contains the same proportion of elements by mass; its statement, history, examples, importance for stoichiometry, and common exceptio…

Lawrencium (Element 103) Lawrencium Lawrencium (Lr, atomic number 103) is a short-lived, synthetic transactinide element produced in particle accelerators and known only from small laboratory samples.

Le Châtelier's principle Le Chatelier's principle A qualitative principle in chemistry and physics describing how a system at equilibrium shifts to oppose applied changes in concentration, pressure, temperature, or other external…

Lead (chemical element) Lead Lead (Pb, atomic number 82) is a dense, malleable heavy metal used historically in pipes, paints, and lead–acid batteries. It is highly toxic, commonly found in the +2 oxidation st…

Lead arsenate Lead arsenate (PbHAsO4) is an inorganic lead arsenate once widely used as an insecticide. It is sparingly soluble, highly toxic, persistent in soils, and remains a remediation conc…

Lead azide (lead(II) azide): properties, uses, and safety Lead azide Lead azide (Pb(N3)2) is a sensitive primary explosive used as a detonator. This article summarizes its chemistry, preparation, applications, hazards, and precautions for handling a…

Lead carbonate (PbCO3): properties, preparation, uses and hazards Lead carbonate Lead carbonate (PbCO3) is an insoluble, toxic lead(II) salt. Found naturally as cerussite and used historically as a white pigment, it decomposes to lead(II) oxide on heating and i…

Lead glass (lead crystal): composition, properties, uses, and safety Lead glass Lead glass, often called lead crystal, contains lead oxide which changes its optical, acoustic and shielding properties. Used for decorative glassware, optics and radiation protect…

Lead nitrate Lead nitrate (Pb(NO3)2) is a water-soluble lead(II) salt used in laboratories and industry; it is crystalline, an oxidiser, and a toxic environmental pollutant requiring careful ha…

Lead oxide Overview of lead oxides: common forms, physical and chemical properties, production methods, uses in industry and art, and health and environmental concerns.

Lead telluride (PbTe): properties, structure, and applications Lead telluride Lead telluride (PbTe) is a narrow-gap semiconductor and rock-salt structured lead chalcogenide used in thermoelectrics and infrared detectors; it combines notable electronic proper…

Lead(II,IV) oxide (lead tetroxide, red lead) Lead(II,IV) oxide Lead(II,IV) oxide (Pb3O4), commonly called red lead or minium, is a red-orange inorganic pigment and industrial lead oxide containing both Pb(II) and Pb(IV); used historically in p…

Lead(II) acetate (sugar of lead) Lead(II) acetate Lead(II) acetate, Pb(C2H3O2)2, is a water‑soluble lead salt historically used in dyes, cosmetics and laboratory tests; it is a toxic compound and is restricted in modern uses.

Lead(II) bromide (plumbous bromide, PbBr2) Lead(II) bromide Lead(II) bromide (PbBr2) is an inorganic lead salt that forms white crystalline precipitates. It is sparingly soluble in water, used as a precursor in materials chemistry, and is t…