Codex @codex  0

By International Union of Pure and Applied Chemistry.

Publisher: International Union of Pure and Applied Chemistry.

This source is credited to an organization.

Online text: iupac.qmul.ac.uk/gtpoc/M.html

Cited passages: Glossary of Terms Used in Physical Organic Chemistry, IUPAC Recommendations 1994, entry “molecularity”: elementary event and exclusion of solvation medium.

By International Union of Pure and Applied Chemistry.

Publisher: International Union of Pure and Applied Chemistry.

This source is credited to an organization.

Online text: iupac.qmul.ac.uk/gtpoc/NO.html

Cited passages: Glossary of Terms Used in Physical Organic Chemistry, IUPAC Recommendations 1994, entry “order of reaction”, final paragraphs: elementary versus stepwise reactions; Glossary of Terms Used in Physical Organic Chemistry, IUPAC Recommendations 1994, entry “order of reaction”: constant B, observed coefficient and pseudo-first-order coefficient.

By International Union of Pure and Applied Chemistry.

Publisher: International Union of Pure and Applied Chemistry.

This source is credited to an organization.

Published in Pure and Applied Chemistry, 66, 1077–1184.

Online text: iupac.qmul.ac.uk/gtpoc/R.html

Cited passages: Glossary of Terms Used in Physical Organic Chemistry, IUPAC Recommendations 1994: radical (or free radical), opening definition and metal-ion qualification; Glossary of Terms Used in Physical Organic Chemistry, IUPAC Recommendations 1994: radical ion, benzene examples and dot/charge placement.

By International Union of Pure and Applied Chemistry.

Entry in IUPAC Compendium of Chemical Terminology, fifth edition (Gold Book) by International Union of Pure and Applied Chemistry, issued by International Union of Pure and Applied Chemistry. No individual entry author is credited; editors are not treated as entry authors. The fifth edition and online version 5.0.0 are dated 2025.

Canonical entry: goldbook.iupac.org/terms/view/B00626

Inspected official indexed mirror: mail.goldbook.iupac.org/terms/view/B00626

Cited passages: IUPAC Compendium of Chemical Terminology, fifth edition (Gold Book), Beer–Lambert law: Official indexed mirror mail.goldbook.iupac.org/terms/view/B00626: complete opening definition, both equations, decadic coefficient name, conventional and SI units, spectral-bandwidth qualification, fifth-edition/version citation; Entry names its underlying 1996 glossary, printed p. 2230; underlying recommendation not independently inspected.

Entry I02938 in IUPAC Compendium of Chemical Terminology, fifth edition (Gold Book) by International Union of Pure and Applied Chemistry, issued by International Union of Pure and Applied Chemistry. No individual entry author is credited; editors and authors of underlying recommendations are not treated as entry authors. The citation gives 2025 for the fifth edition and online version 5.0.0.

Inspected official indexed entry: goldbook.iupac.org/terms/view/I02938/plain

Canonical entry: goldbook.iupac.org/terms/view/I02938

DOI: doi.org/10.1351/goldbook.I02938

Cited passages: Definition; Source; Citation. The underlying 1994 recommendation, p. 543, is cited by the entry and was not independently inspected. Direct entry retrieval failed; the complete official indexed text was inspected.

Entry in IUPAC Compendium of Chemical Terminology, fifth edition (Gold Book) by International Union of Pure and Applied Chemistry, issued by International Union of Pure and Applied Chemistry. No individual entry author is established. The official citation identifies online version 5.0.0, 2025; this is a compendium version date. The entry cites the Orange Book, second edition, p. 48 as its underlying source.

Online text: goldbook.iupac.org/terms/view/S05924/1000

Metadata verification: Official indexed entry and citation; direct request unavailable

Cited passages: Definition paragraphs: primary standard, secondary standard solution; underlying source Orange Book, second edition, p. 48.

By International Union of Pure and Applied Chemistry.

Publisher: International Union of Pure and Applied Chemistry.

In the International Union of Pure and Applied Chemistry (IUPAC) mass spectrometry convention, a molecular ion is formed by removing or adding one or more electrons to a molecule without fragmentation of its molecular structure.^[ref] For example, removing one electron from intact water gives ${\mathrm{H}}_2{\mathrm{O}}^{\bullet +}$: two hydrogen and one oxygen chemical atom, total electric charge $+e$, and an unpaired electron, hence a radical cation. Atom inventory, net electric charge, and electronic state are separate pieces of information. Hydronium, ${\mathrm{H}}_3{\mathrm{O}}^{+}$, has a different inventory; it is a polyatomic ion, rather than the molecular ion obtained by electron removal from water.

A molecule, using the International Union of Pure and Applied Chemistry (IUPAC) convention, is an electrically neutral entity containing two or more chemical atoms. Its constituents form a bound unit through chemical bonds; merely drawing a boundary around neighboring particles does not make a molecule. The neutrality requirement concerns total electric charge, not the absence of internal charge separation: water is a polar molecule with zero total electric charge.^[ref]

One water molecule, ${\mathrm{H}}_2\mathrm{O}$, contains two hydrogen and one oxygen chemical atom. One molecular oxygen molecule, ${\mathrm{O}}_2$, contains two oxygen chemical atoms; a molecule need not contain different chemical elements. One carbon dioxide molecule, $\mathrm{C}{\mathrm{O}}_2$, contains one carbon and two oxygen chemical atoms. The molecular formula records these inventories, while molecular geometry describes their arrangement. Water and carbon dioxide are chemical compounds; molecular oxygen is a form of one chemical element.

Ordinary crystalline sodium chloride, $\mathrm{NaCl}$, contains an extended arrangement of sodium cations $\mathrm{N}{\mathrm{a}}^{+}$ and chlorine anions $\mathrm{C}{\mathrm{l}}^{-}$. Its formula unit specifies one of each for compositional accounting, without selecting a unique isolated pair. Bulk neutrality therefore does not imply a material consists of neutral molecules. This statement concerns the ionic crystal; the physical state and conditions matter when deciding what particles a chemical formula represents.^[ref]

A polyatomic ion is a charged bound group of chemical atoms, such as hydronium, ${\mathrm{H}}_3{\mathrm{O}}^{+}$. A molecular ion formed by removing an electron from intact water, ${\mathrm{H}}_2{\mathrm{O}}^{\bullet +}$, retains the same atom inventory but has net electric charge $+e$. Neither satisfies the neutral-molecule definition. Distinguishing these entities makes molecular count and amount of substance and mass spectrometry interpretable: say whether the count is of chemical atoms, neutral molecules, ions, or formula units.

The useful surprise is that a molecule can be treated as one particle for motion and counting while retaining internal structure. Its molar mass connects a particle inventory to bulk mass; molecular rotation and molecular vibration reveal internal organization. The continuum approximation uses bulk fields in place of individual molecular positions and motions.