Glossary of chemical terms

macromolecule
	Macromolecule is a molecule of high relative molecular mass (molecular weight), the structure of which essentially comprises the multiple repetition of units derived, actually or conceptually, from molecules of low relative molecular mass.
mass
	Mass (m) is the quantity of matter contained in a particle or body regardless of its location in the universe. Mass is constant, whereas weight is affected by the distance of a body from the center of the Earth (or of other planet). The SI unit is kilogram. According to the Einstein equation E = mc2 all forms of energy possess a mass equivalent.
mass fraction
	Mass fraction (wA) is the ratio of the mass of substance A to the total mass of a mixture.
mass number
	Mass number (A) is a characteristic property of a specific isotope of an element, equal to the sum of the number of protons and neutrons in the nucleus.
mass spectrometry
	Mass spectrometry is an analytical technique in which ions are separated according to the mass/charge (m/e) ratio and detected by a suitable detector. In a mass spectrometer a sample is ionized and the positive ions produced are accelerated into a high-vacuum region containing electric and magnetic fields. These fields deflect and focus the ions onto a detector. A mass spectrum is thus obtained consisting of a series of peaks of variable intensity to which m/e values can be assigned. Different molecules can be identified by their characteristic pattern of lines.
mean free path
	Mean free path is the average distance a gas molecule travels between collisions.
Meissner effect
	Meissner effect is the complete exclusion of magnetic induction from the interior of a superconductor.
melting point
	Melting point (or freezing point) is the temperature at which the solid and liquid phases of a substance are in equilibrium at a specified pressure (normally taken to be atmospheric unless stated otherwise). A pure substance under standard condition of pressure has a single reproducible melting point. The terms melting point and freezing point are often used interchangeably, depending on whether the substance is being heated or cooled.
meniscus
	Meniscus is the concave curve of a liquid surface in a graduate or narrow tube. Caused by surface tension.
mercaptans
	Mercaptans are a traditional term abandoned by IUPAC, synonymous with thiols. This term is still widely used.
metalloid
	Metalloid (semimetal) is any of a class of chemical elements intermediate in properties between metals and nonmetals. The classification is not clear cut, but typical metalloids are boron (B), silicon (Si), germanium (Ge), arsenic (As), and tellurium (Te). They are electrical semiconductors and their oxides are amphoteric.
metals
	Metals are a material in which the highest occupied energy band (conduction band) is only partially filled with electrons. Their physical properties generally include: - They are good conductors of heat and electricity. The electrical conductivity of metals generally decreases with temperature. - They are malleable and ductile in their solid state. - They show metallic luster. - They are opaque. - They have high density. - They are solids (except mercury) - They have crystal structure in which each atom is surrounded by eight to twelve near neighbors Their chemical properties generally are: - They have one to four valence electrons. - They have low ionization potentials; they readily lose electrons. - They are good reducing agents. - They have hydroxides which are bases or amphoteric. - They are electropositive. Metallic characteristics of the elements decrease and non-metallic characteristics increase with the increase of valence electrons. Also metallic characteristics increase with the number of electron shells. Therefore, there is no sharp dividing line between the metals and the non-metals. Of the 113 elements now known, only 17 show primarily non-metallic characteristics, 7 others are metalloids, and 89 may be classed as metals.
metre
	Metre (m) is the SI base unit of length. The meter is the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 s. This definition, adopted by the General Conference on Weights and Measure in October 1983, replaced the 1967 definition based on the krypton lamp.
mho
	Mho is an archaic name for the SI unit siemens (reciprocal ohm).
micelle
	Micelle is an electrically charged colloidal particle, usually organic in nature, composed of aggregates of large molecules, e.g., in soaps and surfactants. For aqueous solutions, the hydrophilic end of the molecule is on the surface of the micelle, while the hydrophobic end (often a hydrocarbon chain) points toward the center.
micron
	Micron (μ) is an obsolete name for micrometer (μm).
millimeter of mercury
	Millimeter of mercury (mmHg) is a non-SI unit of pressure, equal to 133.322 Pa. The name is generally considered interchangeable with torr.
molality
	Molality or molal concentration (b; formerly m) is a concentration in which the amount of solute is stated in moles and the amount of solvent in kilograms. The unit of molality is mol kg-1.
molar
	Denoting that an extensive physical property is being expressed per amount of substance, usually per mole.
molar mass
	Molar mass is the mass of one mole of a substance. M = m/n It is normally expressed in units of g mol-1, in which case its numerical value is identical with the relative molecular mass.
molar quantity
	Molar quantity is often convenient to express an extensive quantity (e.g., volume, enthalpy, heat capacity, etc.) as the actual value divided by amount of substance (number of moles). The resulting quantity is called molar volume, molar enthalpy, etc.
molar volume
	Molar volume is the volume occupied by substance per unit amount of substance. The volume of the gas at 0 °C and 101 325 Pa is 22.4 dm3mol-1.
molarity
	Formerly name for concentration.
mole
	Mole (mol) is the SI base unit of amount of substance. The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kg of carbon 12. When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particules, or specified groups of such particles. In this definition, it is understood that the carbon 12 atoms are unbound, at rest and in their ground state.
mole fraction
	Mole fraction (xA) is the ratio of the amount of substance (number of moles) of substance A to the total amount of substance in a mixture.
molecular weight
	See Relative molecular mass
molecule
	Molecule is the smallest part of a chemical compound that can take part in a chemical reaction. The atoms of a molecule are held together by chemical bonds.
momentum
	Momentum (p) is the product of mass and velocity (p = m∙v).
monomer
	Monomer is a simple molecule which is capable of combining with a number of like or unlike molecules to form a polymer. Monomer is repeating structure unit within a polymer.
monosaccharides
	Monosaccharide is a charbohydrate that cannot be split into smaller units by the action of dilute acids. Monosaccharide is any of several simple sugars having the formula C6H12O6; the best-known are glucose, fructose, and galactose. Monosaccharides combine to form more-complex sugars known as oligo- and polysaccharide.

 

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