Macromolecule
A macromolecule is a very large molecule, typically with a molecular weight greater than 10,000 daltons, composed of many repeating structural units (monomers) covalently bonded to…
Chemical Glossary — Letter M
76 chemicals found starting with "M"
Magnesium
Magnesium is a shiny grey alkaline earth metal, atomic number 12. Eighth most abundant element in Earth crust. Essential for life - central atom in chlorophyll. Burns with intensel…
Magnetic Quantum Number
The quantum number (mₗ) that specifies the orientation of an atomic orbital in space relative to a magnetic field. For a subshell with angular momentum quantum number l, mₗ takes i…
Main Group Elements
Main group elements are the elements in Groups 1, 2, and 13–18 of the periodic table (s-block and p-block elements). They include alkali metals, alkaline earth metals, metalloids, …
Manganese
Manganese is a hard, brittle grey-white transition metal, atomic number 25. Essential trace element for all known living organisms. Important in steel production and as an oxidant …
Manometer
A device used to measure the pressure of a gas or liquid. Open-arm manometers measure gauge pressure relative to atmospheric pressure; closed-arm manometers measure absolute pressu…
Mass
Mass is a fundamental property of matter that measures the amount of substance in an object and its resistance to acceleration (inertia). In chemistry, mass is most commonly expres…
Mass Action Expression
The mass action expression is the ratio of the concentrations (or partial pressures) of products to reactants, each raised to the power of its stoichiometric coefficient, for a giv…
Mass Defect
Mass defect is the difference between the calculated mass of an atomic nucleus (sum of the masses of its component protons and neutrons) and the actual measured mass of that nucleu…
Mass Deficiency
Mass deficiency (or mass defect) is the difference between the mass of an atomic nucleus and the sum of the masses of its constituent protons and neutrons when separated. This mass…
Mass Number
The mass number (A) of a nuclide is the total number of protons and neutrons (nucleons) in its nucleus. It is used together with the atomic number (Z) to specify a particular isoto…
Mass Number
The total number of protons and neutrons (nucleons) in the nucleus of an atom, denoted A. The mass number is written as a superscript before the element symbol (e.g., ¹²C). Isotope…
Mass Spectrometer
A mass spectrometer is an analytical instrument that separates ions according to their mass-to-charge ratio (m/z) after vaporizing and ionizing a sample. The technique involves ion…
Mass Spectrometry
An analytical technique that separates ions by mass-to-charge ratio (m/z) to determine molecular masses and structural information. The sample is ionized, accelerated, and deflecte…
Matter
Matter is anything that has mass and occupies space (has volume). In chemistry, matter exists in four main states: solid, liquid, gas, and plasma. Matter is composed of atoms and m…
Matter
Anything that has mass and occupies space. Matter exists in four states: solid, liquid, gas, and plasma. Chemistry is the study of the properties and transformations of matter. All…
Mean Free Path
The mean free path is the average distance a particle (molecule, electron, photon) travels between successive collisions with other particles. In gases, it depends on the size of t…
Mechanism
A detailed, step-by-step description of the sequence of bond-breaking and bond-forming events that occur during a chemical reaction. Mechanisms show the movement of electrons using…
Meitnerium
Meitnerium is a synthetic radioactive transactinide element named after physicist Lise Meitner. Expected to behave similarly to iridium. First synthesised in 1982 at GSI Darmstadt.
Melting Point
The melting point is the temperature at which a solid converts to a liquid at a given pressure (usually 1 atm). At the melting point, solid and liquid phases are in dynamic equilib…
Melting Point
The temperature at which a solid changes to a liquid at a given pressure. Pure substances have sharp, characteristic melting points. Impurities lower and broaden the melting point …
Mendelevium
Mendelevium is a synthetic radioactive actinide named after Dmitri Mendeleev, creator of the periodic table. First synthesised in 1955 at Berkeley by bombarding einsteinium-253 wit…
Meniscus
The meniscus is the curved surface of a liquid in a container caused by surface tension and the intermolecular forces between the liquid and the container walls. A concave meniscus…
Mercury
Mercury is a silvery-white liquid metal at room temperature, atomic number 80. The only metallic element that is liquid at standard conditions. Highly toxic - accumulates in the fo…
Metal
A metal is a material (element, compound, or alloy) that typically exhibits high electrical conductivity, thermal conductivity, metallic luster, malleability, ductility, and the ab…
Metallic Bond
The type of chemical bonding in metals, characterized by mobile electrons (electron sea) surrounding a lattice of positive metal ions. Metallic bonds explain the high electrical an…
Metallic Bonding
Metallic bonding is the type of chemical bonding found in metals, in which positively charged metal ions (cations) are surrounded by and attracted to a delocalized sea of mobile va…
Metallic Character
The tendency of an element to exhibit metal-like properties such as forming positive ions, conducting electricity, and having lustrous appearance. Metallic character decreases acro…
Metallic Conduction
Metallic conduction is the flow of electric current through metals by the movement of delocalized (free) electrons through the metallic lattice. Unlike electrolytic conduction, no …
Metalloid
An element with properties intermediate between metals and nonmetals, also called a semimetal. Metalloids include boron, silicon, germanium, arsenic, antimony, tellurium, and polon…
Metalloids
Metalloids (also called semimetals) are elements with properties intermediate between those of metals and nonmetals, typically found along the staircase boundary on the periodic ta…
Metallurgy
Metallurgy is the science and technology of extracting metals from their ores, refining them, and preparing them for practical use. It encompasses pyrometallurgy (high-temperature …
Metathesis Reactions
A metathesis reaction (double displacement reaction) is a chemical reaction in which two compounds exchange ions or bonds to form two new compounds, without a change in the oxidati…
Method Of Initial Rates
The method of initial rates is an experimental technique used to determine the order of a chemical reaction with respect to each reactant by measuring the initial rate of reaction …
Miscibility
Miscibility describes the ability of two liquids to mix in all proportions to form a homogeneous solution. Liquids are miscible if their intermolecular forces are compatible ('like…
Miscibility
The property of liquids to mix in all proportions without separating into two phases. Polar liquids are generally miscible with polar liquids (e.g., ethanol and water), and nonpola…
Miscibility Gap
A miscibility gap is a region in a phase diagram where two liquids (or solids) are not completely miscible and form two separate phases. Outside the miscibility gap, the components…
Miscible
Describes liquids that can be mixed in all proportions to form a homogeneous solution. Ethanol and water are miscible. Miscibility depends on intermolecular forces: like dissolves …
Mixture
A mixture is a combination of two or more substances that are physically combined but not chemically bonded, and that retain their individual properties. Mixtures can be separated …
Mixture
A combination of two or more substances that are physically combined but not chemically bonded. Mixtures retain the properties of their components and can be separated by physical …
Moderator
A neutron moderator is a material used in nuclear reactors to slow down (moderate) fast neutrons produced by fission to thermal energies, making them more effective at causing furt…
Mohr's Salt
Ammonium iron(II) sulfate hexahydrate, (NH₄)₂Fe(SO₄)₂·6H₂O. It is a primary standard in volumetric analysis because it is stable in air (iron(II) in this salt is resistant to oxida…
Moiety
A term used in chemistry to describe a part or functional unit within a larger molecule, particularly in organic and biochemistry. For example, the phenyl moiety refers to the C₆H₅…
Molality
Molality (m) is a measure of solute concentration expressed as the number of moles of solute per kilogram of solvent. Unlike molarity, molality is independent of temperature becaus…
Molality
A concentration unit defined as the number of moles of solute per kilogram of solvent (mol/kg), symbol m. Unlike molarity, molality does not change with temperature since it is bas…
Molar Conductivity
The conductivity of a solution containing one mole of electrolyte per liter, measured in S·cm²/mol. Molar conductivity increases with dilution for weak electrolytes (as more dissoc…
Molar Mass
The mass of one mole of a substance, expressed in g/mol. Numerically equal to the atomic or molecular mass in atomic mass units (amu). Molar mass is used to convert between grams a…
Molar Solubility
Molar solubility is the number of moles of a sparingly soluble salt that dissolves per liter of solution to form a saturated solution at a given temperature. It is related to the s…
Molar Volume
The volume occupied by one mole of a substance. At STP (0°C, 1 atm), one mole of an ideal gas occupies 22.4 L. At standard conditions (25°C, 1 bar), the molar volume is 24.8 L. Mol…
Molarity
Molarity (M) is the most common measure of solution concentration, defined as the number of moles of solute dissolved per litre of solution (mol/L). It is used to calculate the amo…
Molarity
A concentration unit defined as the number of moles of solute per liter of solution (mol/L), symbol M. Molarity is the most common concentration unit in chemistry. It changes with …
Mole
The SI unit for amount of substance, defined as exactly 6.02214076 × 10²³ elementary entities (Avogadro's number). One mole of any substance contains the same number of formula uni…
Mole Fraction
Mole fraction (χ) is the ratio of the number of moles of one component to the total number of moles of all components in a mixture. Mole fractions are dimensionless and sum to 1 fo…
Mole Fraction
A dimensionless concentration unit defined as the ratio of the moles of one component to the total moles of all components in a mixture. Mole fractions range from 0 to 1 and always…
Mole Ratio
The ratio of moles of one substance to moles of another substance in a balanced chemical equation. Mole ratios are used as conversion factors in stoichiometric calculations to find…
Molecular Equation
A molecular equation is a chemical equation that shows all reactants and products as complete, neutral formulas without indicating whether substances are ionic or covalent in solut…
Molecular Formula
A molecular formula shows the exact number of atoms of each element present in one molecule of a compound. It is derived from the empirical formula by multiplying by an integer fac…
Molecular Formula
A chemical formula showing the actual number of atoms of each element in one molecule of a compound, without indicating structure. For example, glucose is C₆H₁₂O₆. The molecular fo…
Molecular Geometry
Molecular geometry is the three-dimensional arrangement of atoms in a molecule. It is determined by the Valence Shell Electron Pair Repulsion (VSEPR) theory, which states that elec…
Molecular Ion
The ion formed in mass spectrometry when a molecule loses one electron to form M⁺ (radical cation). The molecular ion peak (M⁺) in a mass spectrum corresponds to the molecular mass…
Molecular Orbital
A molecular orbital (MO) is a mathematical function describing the wave-like behavior of an electron in a molecule, formed by the linear combination of atomic orbitals (LCAO) from …
Molecular Orbital Theory
Molecular orbital (MO) theory describes the electronic structure of molecules by combining atomic orbitals to form molecular orbitals that are delocalised over the entire molecule.…
Molecular Orbital Theory
A theory describing chemical bonding in which atomic orbitals combine to form molecular orbitals that extend over the entire molecule. Bonding MOs lower energy; antibonding MOs rai…
Molecular Weight
Molecular weight (molecular mass) is the sum of the atomic masses of all atoms in a molecule, expressed in atomic mass units (amu or u), which are numerically equal to daltons (Da)…
Molecular Weight
The sum of the atomic weights of all atoms in a molecule, expressed in atomic mass units (amu) or g/mol. Equivalent to molar mass. Determined experimentally by mass spectrometry, o…
Molecule
A molecule is the smallest unit of a chemical compound that retains the compound's chemical properties, consisting of two or more atoms bonded together by covalent bonds. Molecules…
Molecule
The smallest unit of a covalent compound that retains its chemical identity. Molecules consist of two or more atoms held together by covalent bonds. Diatomic molecules (H₂, O₂, N₂)…
Molten
Describes a substance in the liquid state due to heating beyond its melting point. Molten ionic compounds conduct electricity because their ions are mobile. Electrolysis of molten …
Molybdenum
Molybdenum is a silvery, hard transition metal, atomic number 42. Has the sixth-highest melting point of all elements. Essential trace element for most organisms (component of moly…
Monobasic Acid
An acid that has only one replaceable hydrogen atom per molecule. It reacts with bases in a 1:1 molar ratio. Examples include hydrochloric acid (HCl) and nitric acid (HNO₃). Equiva…
Monomer
The small, repeating subunit from which a polymer is built. Monomers undergo polymerization reactions to form long chain polymers. Examples include ethylene (monomer of polyethylen…
Monoprotic Acid
A monoprotic acid (monobasic acid) is an acid that can donate only one proton (H⁺) per molecule in an acid–base reaction. Examples include hydrochloric acid (HCl), nitric acid (HNO…
Monoprotic Acid
An acid that can donate only one proton (H⁺) per molecule in an acid-base reaction. Examples include hydrochloric acid (HCl), nitric acid (HNO₃), and acetic acid (CH₃COOH). Monopro…
Moscovium
Moscovium is a synthetic radioactive element named after Moscow Oblast, Russia. First synthesised in 2003 through collaboration between the Joint Institute for Nuclear Research in …
Mother Nuclide
The initial radioactive isotope (parent nuclide) that undergoes radioactive decay to produce a daughter nuclide. For example, uranium-238 is the mother nuclide that decays through …
Multiple Bond
A chemical bond in which two atoms share more than one pair of electrons. Double bonds consist of one sigma and one pi bond; triple bonds consist of one sigma and two pi bonds. Mul…
About Chemicals Starting With M
This page lists all chemicals in our database beginning with the letter M. Each entry provides the chemical formula, CAS registry number, physical and chemical properties, common uses, and safety information. Use the alphabetical navigation above to browse other letters, or use the search function to find a specific chemical quickly.
Our chemical glossary covers acids, bases, salts, organic compounds, inorganic compounds, solvents, and many more categories. Click on any chemical name to view its full detailed profile.