GLOSSARY
The words this atlas uses.
Short definitions for the terms that recur across element profiles, journeys and articles. Each definition names its source and the boundary of its use here; none of them replaces the standard definition it cites.
- alloy
An alloy combines metals with one another or with selected nonmetal elements, as in carbon steel.
This describes the metallic materials discussed here; alloys need not consist only of metals.
AlloyNational Institute of Standards and Technology (OSAC Lexicon; ASTM E1732 terminology) · Simplified
- catalyst
A catalyst speeds a chemical reaction and is regenerated through the reaction sequence.
The formal definition also specifies that the catalyst does not change the overall standard Gibbs energy change of the reaction.
IUPAC Gold Book: catalystInternational Union of Pure and Applied Chemistry · Simplified
- isotope
Isotopes are forms of an element whose nuclei share a proton count but differ in neutron count.
This paraphrases the formal atomic-number and mass-number definition in particle language.
IUPAC Gold Book: isotopesInternational Union of Pure and Applied Chemistry · Simplified
- semiconductor
A semiconductor is a material with controllable electrical charge-carrier density and conductivity usually between that of metals and insulators.
The conductivity range is typical, not a fixed boundary that every sample must satisfy under every condition.
IUPAC Gold Book: semiconductorInternational Union of Pure and Applied Chemistry · Simplified
- electrolyte
An electrolyte is a medium in which moving ions carry electrical current.
Here the term means the conducting medium, which may be liquid or solid; it can also name the substance supplying ions.
IUPAC Gold Book: electrolyteInternational Union of Pure and Applied Chemistry · Simplified; conducting-medium sense
- ion
An ion is an atom or group of atoms with an overall positive or negative electric charge.
Includes single-atom ions and molecular ions; the charge describes the particle as a whole.
IUPAC Gold Book: ionInternational Union of Pure and Applied Chemistry · Simplified
- crystal
A crystal is a solid whose atoms, ions or molecules have long-range spatial order.
Order need not mean a perfectly repeating three-dimensional pattern; the definition also includes aperiodic crystals.
Crystal — Online Dictionary of CrystallographyInternational Union of Crystallography · Simplified direct-space definition
- corrosion
Corrosion is an irreversible reaction at a material’s interface with its environment that consumes the material or dissolves an environmental component into it.
Corrosion is not limited to metals; purely mechanical wear is excluded from the formal definition.
IUPAC Gold Book: corrosionInternational Union of Pure and Applied Chemistry · Paraphrase of formal definition
- radioactivity
Radioactivity is the spontaneous transformation of unstable atomic nuclei, accompanied by the emission of radiation.
A sample’s activity measures the rate of these transformations.
What Is Radioactivity?U.S. Department of Energy — ACHRE report archive · Simplified
- half-life
A radioactive half-life is the time in which half the nuclei of a particular isotope in a large sample are expected to decay.
This is a statistical population measure, not a fixed lifetime for each nucleus.
What Is Radioactivity? — What is radioactive half-life?U.S. Department of Energy — ACHRE report archive · Simplified; radioactive-decay sense
- oxidation
Oxidation is the loss of electrons by a chemical species, or an increase in an atom’s assigned oxidation number.
Adding oxygen is one familiar example; oxidation does not always require oxygen, and electron loss can be formal bookkeeping.
IUPAC Gold Book: oxidationInternational Union of Pure and Applied Chemistry · Simplified formal definition
- doping
Doping deliberately adds selected impurities to a semiconductor to change its electrical properties.
This definition is scoped to impurity doping, the fabrication process described in the silicon article.
PNDIODES — Power Nitride Doping Innovation Offers Devices Enabling SWITCHESU.S. Department of Energy, ARPA-E · Simplified; impurity-doping sense
- nucleus
The dense center of an atom, holding its protons and neutrons. The proton count fixes which element the atom is.
A nucleus is described here by its particle counts, not by a solved structure.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- proton
A positively charged particle in the nucleus. The number of protons is the atomic number and defines the element.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- neutron
An uncharged particle in the nucleus. Changing the neutron count gives a different isotope of the same element.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- electron
A negatively charged particle outside the nucleus. Electron arrangement governs how an element bonds and conducts.
Shell counts describe an arrangement; they do not draw electron paths.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- valence
The outermost electrons of an atom, and the combining behavior that follows from them.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- oxidation state
A bookkeeping charge assigned to an atom in a compound, used to track where electrons have gone in a reaction.
A formal accounting device rather than a measured charge.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- allotrope
A distinct structural form of the same element, such as graphite and diamond for carbon.
Allotropes share an element and differ in properties; a property of one is not a property of the element.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- lattice
The repeating arrangement of atoms in a crystalline solid.
Illustrations in this atlas are idealized fragments unless a structure record is cited.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- unit cell
The smallest repeating block of a crystal lattice, from which the whole structure is built by repetition.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- grain
A region of a solid where the lattice keeps one orientation. Where two grains meet is a grain boundary.
Grain structure depends on processing history, not on composition alone.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- dislocation
A line defect in a crystal. Metals deform largely by dislocations moving, which is why a pure metal can be soft.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- annealing
Heating a material and cooling it in a controlled way to change its internal structure, usually to relieve stress or soften it.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- ductile
Able to be drawn or stretched without breaking. The opposite behavior is brittle.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- brittle
Fracturing with little deformation beforehand.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- anode
The electrode where oxidation happens: the place electrons leave the chemistry and enter the circuit.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- cathode
The electrode where reduction happens: the place electrons return from the circuit into the chemistry.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- electrode
A conductor through which current enters or leaves a chemical system.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- electrolysis
Driving a chemical change by passing current through a conducting liquid or melt.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- redox
A reaction in which electrons move from one species to another. One side is oxidized as the other is reduced.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- reduction
Gain of electrons by a species, the counterpart of oxidation.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- precipitate
A solid that forms and separates out of a solution.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- solubility
How much of a substance dissolves in a given solvent under stated conditions.
Solubility is condition-dependent; a figure without its conditions is incomplete.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- solute
The substance dissolved in a solvent.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- solvent
The liquid in which a solute dissolves.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- hydration
The association of water molecules with a dissolved ion or molecule.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- ligand
A molecule or ion bound to a central metal atom in a complex.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- coordination
The arrangement and count of neighbors bonded to a central atom.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- chelate
A ligand that grips a metal ion at more than one point.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- enzyme
A biological catalyst, usually a protein, that speeds a specific reaction.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- protein
A chain of amino acids folded into a working shape. Many carry a metal at a specific site.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- polymer
A material built from long repeating molecular chains.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- cross-link
A bond joining one polymer chain to another, which stiffens the material and limits flow.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- spectrum
Signal intensity arranged by wavelength, energy or mass, used to identify what produced it.
A match to a line list identifies a candidate, not an abundance.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- wavelength
The distance between repeats of a wave.
Air and vacuum wavelengths are labeled separately in this atlas and are not interchangeable.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- photon
A single quantum of light, carrying an energy set by its wavelength.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- emission
Light released as a system drops to a lower energy state.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- absorption
Light taken up as a system rises to a higher energy state.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- diffraction
Interference of waves scattered by an ordered structure, whose pattern constrains the arrangement.
A pattern constrains a structure rather than determining it uniquely.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- scattering
Redirection of waves or particles by matter.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- resolution
The smallest separation an instrument can still show as two things rather than one.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- calibration
Relating an instrument's reading to a known reference so a number means something.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- detector
The part of an instrument that turns a physical signal into a recordable one.
Detector response is part of the evidence, not a neutral window onto it.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- band gap
The energy step between the filled and empty electron states of a semiconductor, which sets what light it absorbs or emits.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- dopant
A deliberately added impurity that changes a semiconductor's carrier population.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- charge carrier
A mobile electron or hole that carries current through a material.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- superconductivity
Loss of electrical resistance below a characteristic temperature.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- ferromagnetism
Magnetic ordering in which atomic moments align, giving a material a magnetisation of its own.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- ore
A rock or mineral from which an element can be extracted at a worthwhile concentration.
Whether a deposit is an ore depends on economics and method, not on composition alone.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- mineral
A naturally occurring solid with a definite composition and an ordered structure.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- refining
Removing unwanted components from a crude material to reach a required purity.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- abundance
How much of an element is present in a stated reservoir, such as the crust, seawater or the Sun.
An abundance is meaningless without its reservoir and units.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- decay
Spontaneous transformation of an unstable nucleus, emitting radiation and leaving a different nuclide.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- alpha decay
Decay by emitting a helium nucleus.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- beta decay
Decay in which a neutron and proton convert into one another, emitting an electron or positron.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- gamma ray
High-energy light emitted as a nucleus settles to a lower energy state.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- fission
Splitting of a heavy nucleus into lighter ones, releasing energy and neutrons.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- fusion
Joining of light nuclei into a heavier one, the energy source of stars.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- phase
A physically distinct, uniform form of matter, such as a solid, a liquid, or one solid structure among several.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- equilibrium
A condition where opposing changes proceed at matching rates, so measured amounts stop changing.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- catalysis
Speeding a reaction with a substance that is not consumed by it.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- adsorption
Accumulation of a substance on a surface, as distinct from dissolving into a bulk.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- membrane
A barrier that lets some species through and holds others back.
A biological membrane and a filtration membrane are different systems; the word is shared.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- titration
Measuring an unknown amount by adding a reagent until a reaction is just complete.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- buffer
A solution that resists change in acidity when acid or base is added.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- oxide
A compound of an element with oxygen.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- sulfide
A compound of an element with sulfur; a common form for metal ores.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- carbonate
A compound containing the carbonate group, common in shells, limestone and scale.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- silicate
A compound built from silicon-oxygen units; the main constituent of most rocks.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- halide
A compound of an element with a halogen.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
- hydroxide
A compound containing the hydroxide group.
atlas working definition · explains how this atlas uses the word; no standard authority is claimed
82 terms are defined so far. Twelve cited definitions include source checks; the working definitions provide editorial explanations..