Chemistry

Manganese dioxide Manganese dioxide (MnO2) is a black inorganic oxide of manganese in the +4 oxidation state, occurring naturally as pyrolusite and used as an oxidizer, catalyst and depolarizer in b…

Manganese fluoride Inorganic fluorides of manganese in oxidation states II–IV. Covers major compounds (MnF2, MnF3, MnF4), their structures, properties, preparation, uses and safety considerations.

Manganese oxide Overview of manganese oxides: common chemical forms, structures, properties, natural occurrence, industrial uses, environmental roles and safety considerations across oxidation sta…

Manganese(II) chloride: properties, preparation, uses, and safety Manganese(II) chloride Manganese(II) chloride (MnCl2) is a pale pink inorganic salt used as a precursor to other manganese compounds, in laboratories and industry; it exists in anhydrous and hydrated for…

Manganese(II) fluoride (MnF2): properties, structure and applications Manganese(II) fluoride Overview of manganese(II) fluoride (MnF2): its rutile-type crystal structure, Mn2+ characteristics, synthesis, magnetic behavior, solubility, and applications in fluorination and o…

Manganese(II) oxide (MnO) — properties, preparation, and uses Manganese(II) oxide Manganese(II) oxide (MnO) is a common manganese compound in the +2 oxidation state, used as a precursor to other manganese chemicals, in ceramics and pigments, and studied in mater…

Manganese(II) sulfate An overview of manganese(II) sulfate (MnSO4): its properties, hydrated forms, production routes, common uses in agriculture and industry, typical reactions, and basic safety consid…

Manganese(III) fluoride (MnF3) Manganese(III) fluoride Inorganic manganese fluoride in the +3 oxidation state. A pink–violet crystalline solid used as an oxidizing and fluorinating reagent; hydrolyzes to release HF and requires strict…

Manganese(III) oxide (Mn2O3) Manganese(III) oxide Mn2O3 is a brown–black inorganic oxide of manganese in the +3 oxidation state. It occurs as a solid with distinct polymorphs, forms during reduction of MnO2, and is used as a precu…

Manganese(IV) fluoride (MnF4) Manganese(IV) fluoride Manganese(IV) fluoride, MnF4, is a pale blue‑green, highly reactive inorganic fluoride of manganese in the +4 oxidation state used as a strong oxidizer and laboratory fluorinating…

Manganese(VII) oxide (manganese heptoxide, Mn2O7) Manganese(VII) oxide A volatile molecular oxide of manganese in the +7 oxidation state. Mn2O7 is a dark green oily liquid, a very strong oxidizer and shock-sensitive explosive prepared from permanganat…

Mass number (A) Mass number The mass number is the integer count of protons and neutrons in an atomic nucleus. It identifies isotopes, underpins nuclear reactions and dating, and differs from atomic number an…

Mass spectrometry: principles, history, techniques, and applications Mass spectrometry Mass spectrometry is an analytical method that measures mass-to-charge ratios of ions to identify and quantify molecules. This article explains principles, steps, ionization and an…

Mass spectrum: principles, features, and applications Mass spectrum A mass spectrum displays ion intensity against mass-to-charge ratio, revealing molecular masses, fragmentation patterns, isotopic peaks and aiding identification methods from small…

Material (physical substance): types, properties, and uses Material An accessible overview of materials as physical substances: definitions, major classes (metals, polymers, ceramics, composites, textiles), raw vs refined materials, history, proper…

Mauveine: the first synthetic organic dye and its historical impact Mauveine Mauveine (Perkin's mauve) is the first commercially successful synthetic organic dye, discovered in 1856. It transformed textile coloring and launched the modern chemical dye indus…

McLafferty rearrangement A gas-phase fragmentation in mass spectrometry in which a γ-hydrogen transfers to a carbonyl group through a six-membered transition state, producing characteristic fragment ions u…

MDMA (ecstasy, molly): effects, history, risks, and research MDMA Comprehensive overview of MDMA (ecstasy, molly): its chemistry and effects, common forms and adulteration, health risks, legal status, and current medical research directions.

Meitnerium (Element 109) Meitnerium Meitnerium is a synthetic, highly radioactive transition metal with atomic number 109. Produced only in particle accelerators, it has no practical uses and is known from short-live…

Melting: the phase change from solid to liquid Melting Melting is the phase transition in which a solid becomes a liquid when supplied with enough thermal energy; its onset is the melting point and is influenced by pressure, purity and…

Melting point Melting point is the temperature at which a solid becomes a liquid under given pressure. This article explains its physical basis, measurement, influencing factors, common examples…

Mendeleev's predicted elements and their role in the development of the periodic table Mendeleev's predicted elements How Dmitri Mendeleev left gaps in his 1869 periodic table, predicted properties of unknown elements (the 'eka-' series), and how later discoveries confirmed and refined his approac…

Mendelevium (element 101) Mendelevium Mendelevium (Md, atomic number 101) is a synthetic, radioactive transuranic actinide element produced in particle accelerators and used only in research.

Mercury: planet, element, and cultural figure Mercury Overview of Mercury: the innermost planet, the metallic element (Hg), and the Roman deity; covers planetary properties, chemistry and toxicity, cultural roles, history, and modern…

Mercury (element) — Hg, atomic number 80 Mercury (element) Mercury (Hg) is a dense, silvery metal that is liquid at room temperature. Known as quicksilver or hydrargyrum, it has distinctive physical properties, wide historical uses, and se…

Mercury battery A primary electrochemical cell that uses zinc and mercury(II) oxide to produce a steady voltage. Once common in small button cells, it is now largely restricted because of mercury…

Mercury bromide Inorganic compounds of mercury and bromine, mainly mercury(II) bromide (HgBr2) and mercury(I) bromide (Hg2Br2): properties, structures, historical uses and modern safety considerat…

Mercury chloride Overview of the two compounds commonly called mercury chloride (mercuric chloride and mercurous chloride), their properties, history, uses, and health and safety considerations.

Mercury iodide (mercurous and mercuric iodides) Mercury iodide Inorganic compounds of mercury with iodine — chiefly mercury(II) iodide (HgI2) and mercury(I) iodide (Hg2I2). Notable for polymorphism, thermochromism, analytical uses, detector ma…

Mercury sulfate Mercury sulfate refers to two inorganic salts—mercury(II) sulfate (HgSO4) and mercury(I) sulfate (Hg2SO4)—with distinct structures, properties and historical uses; both are highly…

Mercury-vapor lamp An electric gas-discharge lamp in which mercury vapor produces ultraviolet and visible light; used historically for street and industrial lighting, now partly replaced for environm…

Mercury(I) bromide (mercurous bromide, Hg2Br2) Mercury(I) bromide Mercury(I) bromide (Hg2Br2) is a crystalline mercurous salt composed of the dimeric Hg2(2+) cation and bromide. It is toxic, chemically unstable toward oxidation/disproportionation…

Mercury(I) chloride (calomel) Mercury(I) chloride Mercury(I) chloride, commonly called calomel, is Hg2Cl2 — a sparingly soluble mercurous salt with historical medicinal use and modern applications as a reference electrode; it is h…

Mercury(I) fluoride (mercurous fluoride) Mercury(I) fluoride Mercury(I) fluoride, Hg2F2, is a mercurous salt containing the Hg2(2+) dimer and fluoride ions. It is an uncommon, moisture-sensitive inorganic solid of academic interest and notab…

Mercury(I) iodide (Hg2I2) Mercury(I) iodide Mercury(I) iodide, Hg2I2, is a mercurous salt containing the dimeric Hg2(2+) ion and iodide. It is a sparingly soluble, unstable mercury compound with limited modern uses and signi…

Mercury(I) nitrate (mercurous nitrate) Mercury(I) nitrate Mercury(I) nitrate, Hg2(NO3)2, is the mercurous salt containing the dimeric Hg2(2+) cation. It is chemically distinct from mercury(II) compounds and is toxic; it can disproportiona…

Mercury(I) sulfate (mercurous sulfate) Mercury(I) sulfate An overview of mercury(I) sulfate (Hg2SO4): composition, structure, preparation, properties, uses and safety considerations for this toxic mercurous salt.

Mercury(II) bromide (mercuric bromide) Mercury(II) bromide Mercury(II) bromide, HgBr2, is a toxic inorganic compound used historically in photography and chemistry. This article summarizes its structure, properties, applications, preparati…

Mercury(II) chloride (mercuric chloride, corrosive sublimate) Mercury(II) chloride Mercury(II) chloride (HgCl2) is a toxic, covalent mercury salt formerly used as an antiseptic and preservative; it occurs as a white crystalline solid and is regulated due to sever…

Mercury(II) fluoride (mercuric fluoride) Mercury(II) fluoride An overview of mercury(II) fluoride (HgF2): composition, appearance, preparation, chemical behavior, uses in research, and safety/environmental concerns.

Mercury(II) iodide (mercuric iodide) — properties, uses and safety Mercury(II) iodide Mercury(II) iodide (HgI2) is a red crystalline inorganic compound with distinct polymorphs, semiconductor behavior, detector applications, and notable toxicity and chemical reactiv…

Mercury(II) nitrate Mercury(II) nitrate (Hg(NO3)2) is a toxic inorganic salt of divalent mercury and nitrate ions. It is a water-soluble oxidizing compound used historically in hatting and as a labora…

Mercury(II) oxide (HgO) Mercury(II) oxide Mercury(II) oxide, HgO, is an inorganic mercury compound appearing as red or yellow solid. It has historical uses in oxygen preparation and pigments, but is highly toxic and now li…

Mercury(II) sulfate (mercuric sulfate) Mercury(II) sulfate Mercury(II) sulfate (HgSO4) is an inorganic mercury salt used historically as a catalyst in organic reactions; it is a toxic, crystalline compound containing Hg2+ and sulfate anion…

Mercury(II) sulfide (HgS): properties, forms, uses, and safety Mercury(II) sulfide Mercury(II) sulfide (HgS), known as cinnabar or mercuric sulfide, is a naturally occurring mercury ore and historically important pigment; it has distinct polymorphs and poses sign…

Mescaline: natural psychedelic phenethylamine found in cacti and cultural use Mescaline Mescaline is a naturally occurring psychedelic phenethylamine found in several cacti and some legumes. It produces altered perception, has ceremonial uses, and is regulated differe…

Metal: properties, types, history, uses, and metallurgy Metal Metals are elements (or alloys) characterized by conductivity, malleability, luster and structural roles. This article explains their properties, common examples, historical develo…

Metallic Bond: Structure, Properties, and Significance Metallic bond A thorough overview of metallic bonding: its electronic basis, physical effects on metals, models and history, practical consequences for alloys and applications, and distinctions…