Sources and Data Methodology

Every scientific claim links to a typed source ID rather than a repeated ad-hoc citation. We preserve units, conditions, uncertainties, and review dates, and we record provenance at the field or grouped-property level — a single generic page citation is not enough for a table assembled from multiple places.

Source hierarchy (preferred order)

IUPAC — nomenclature, terminology, Gold Book (sourceType: iupac)
CIAAW / IUPAC standard atomic weights — conventional/interval weights, bracketed mass numbers (ciaaw, ciaaw-atomic-weights-2021)
NIST Chemistry WebBook and CODATA 2022 — thermochemistry, spectra, physical constants (nist, nist-constants-2022, nist-webbook)
PubChem — compound identifiers (CID, CAS) and carefully scoped summaries (pubchem, pubchem-periodic-table)
Primary standards bodies / government agencies (government)
ACS educational / safety material and RAMP (acs, acs-safety-ramp)
OSHA, NIOSH, GHS-aligned / SDS sources — safety context (ghs_sds, unece-ghs, osha-chemical)
Peer-reviewed literature for specialized claims (primary)
University / OER for pedagogy where primary data does not explain at learner level (oer, openstax-chemistry-2e)
Curriculum frameworks (NGSS etc.) — mapping only, never a substitute for data (curriculum)

We do not cite search snippets, low-quality SEO pages, anonymous answer sites, AI-generated text, or circular encyclopedia copies as primary evidence. Wikipedia may help locate sources but is not the final authority for disputed numerics.

Source record model

Defined in src/content.config.ts (references collection) and src/content/references/*.md:

Stable source ID (filename without extension), title, organization/authors, publication/container, URL or DOI
sourceType, publication/update year, accessedAt / reviewedAt, version
scopeNote — what the source supports
licenseNote and archiveUrl where lawful and useful
status (active / replaced / unavailable) and replacementId / replacementUrl when superseded

Content records reference sourceIds / referenceIds rather than repeating free-text citations, with optional pinpoint notes for sections/tables/fields.

Property-level provenance

Allowed per field or grouped properties in src/lib/chemistry/datasets-types.ts:

MeasuredValue { value, unit, conditions, uncertainty/range, note, provenance: { sourceId, sourceNote (pinpoint), lastVerified, transformNote } }
AtomicWeight { display, conventional, isInterval, isBracketedMassNumber, massNumber, provenance }
ElementRecord.provenanceNotes / CompoundRecord.provenanceNotes / ReactionRecord.provenanceNotes: Record<field, Provenance>

We preserve: canonical value, unit, uncertainty/range, conditions (T/P/phase/isotope/allotrope/scale), source ID + pinpoint, last verified date, and transformation/rounding note if display differs.
We never imply false precision; we do not average conflicting sources to force agreement.
Missing values remain null with a human-readable note (e.g., "decomposes before boiling"), never 0.

Conflict-resolution rules

Confirm same definition, unit, state, temperature, pressure, isotope, allotrope, and scale.
Prefer the recognized current standard/reference source for the exact property.
Preserve standard intervals and bracketed mass-number conventions.
If defensible sources differ, show a qualified range or choose one with a visible method note.
Mark unknown / not established rather than inventing a value.
Log the decision and reviewer (provenance or change note).
Escalate safety-critical conflicts instead of auto-resolving them.

Live source table — 14 records (14 active)

Each entry shows its stable ID, type, status, and scope. Links point to the authoritative container. See individual rows for access/review dates and version.

Source ID	Title	Type	Year	Status	Scope
iupac-gold	Compendium of Chemical Terminology — Gold Book ↗	iupac	2019 (2019-08)	active	Authoritative IUPAC definitions for chemical terminology. Supports term definitions, Gold Book entries, and usage notes
iupac-periodic-table	IUPAC Periodic Table of Elements ↗	iupac	2024 (2024 active)	active	Authoritative IUPAC periodic table: element names, symbols, group numbering 1-18, block assignment conventions, and plac
ciaaw-atomic-weights-2021	CIAAW Standard Atomic Weights 2021 ↗	ciaaw	2021 (2021)	active	Conventional/interval atomic weights for 118 elements. Supports displayed atomic weights, interval notation, and bracket
nist-atomic-weights	CIAAW Standard Atomic Weights 2021 ↗	ciaaw	2021 (2021)	active	Conventional/interval atomic weights for 118 elements. Supports displayed atomic weights, interval notation, and bracket
nist-2022	NIST Chemistry WebBook — Thermochemical, Spectroscopic and Ion Energetics Reference Data ↗	nist	2022 (WebBook active 2024)	active	Evaluated thermochemistry, phase-change, vibrational, ion energetics and spectra. Used for reaction enthalpy, gas law, a
nist-constants-2022	CODATA Recommended Values of Fundamental Physical Constants: 2022 ↗ doi:10.1103/RevModPhys.93.025010	nist	2022 (2022-CODATA)	active	Definitive CODATA 2022 values for Avogadro constant, gas constant, Boltzmann, Planck, Faraday, etc. Used for calculator
nist-webbook	NIST Chemistry WebBook — Thermochemistry, Phase Change and Spectra ↗	nist	2024 (WebBook 2024)	active	Evaluated constants and spectra; retained alongside nist-2022 as web entry point. Points to thermo and energetics collec
pubchem-periodic-table	PubChem Periodic Table and Element Data ↗ doi:10.1093/nar/gkad408	pubchem	2023 (PubChem 2023)	active	Machine-readable element metadata, identifiers, and broad property summaries. Compound pages provide CID, CAS, and struc
osha-chemical	Occupational Chemical Database and Safety & Health Regulations for Chemical Hazards ↗	government	2024 (OSHA 2024)	active	Workplace chemical exposure and SDS context for hazardous substances. Used for handling, ventilation, and disposal guida
acs-safety-ramp	Guidelines for Chemical Laboratory Safety in Secondary Schools & RAMP Framework ↗	acs	2024 (ACS 2024)	active	Learner-facing safety pedagogy: Recognize, Assess, Minimize, Prepare for emergencies. Supports /safety and all experimen
unece-ghs	Globally Harmonized System of Classification and Labelling of Chemicals (GHS), Rev. 11 ↗	ghs_sds	2025 (Rev. 11 (2025))	active	GHS hazard classes, signal words and pictograms. Referenced for label explanation, SDS orientation, and safety callouts.
chang-gold	Chemistry ↗	textbook	2022 (13th ed. 2022)	active	General chemistry scope and pedagogy cross-check; not a substitute for primary IUPAC/NIST data. Used only where primary
tro-chemistry	Chemistry: Structure and Properties ↗	textbook	2023 (3rd ed. 2023)	active	Pedagogy and concept scope cross-check for introductory college level; primary numeric data remains IUPAC/NIST.
openstax-chemistry-2e	Chemistry 2e — Scope Cross-Check Only ↗	oer	2019 (2e (2019))	active	Open educational resource used solely for scope and sequence cross-check; never as primary for numeric data or safety.

Counts by type: acs: 1 · textbook: 2 · ciaaw: 2 · iupac: 2 · nist: 3 · oer: 1 · government: 1 · pubchem: 1 · ghs_sds: 1

Full source JSON (for audit)

[
  {
    "id": "iupac-gold",
    "title": "Compendium of Chemical Terminology — Gold Book",
    "authors": [
      "IUPAC"
    ],
    "organization": "International Union of Pure and Applied Chemistry",
    "publisher": "IUPAC",
    "url": "https://goldbook.iupac.org/",
    "year": 2019,
    "accessedAt": "2026-08-21T00:00:00.000Z",
    "reviewedAt": "2026-08-22T00:00:00.000Z",
    "version": "2019-08",
    "sourceType": "iupac",
    "status": "active",
    "scopeNote": "Authoritative IUPAC definitions for chemical terminology. Supports term definitions, Gold Book entries, and usage notes across glossary and lessons.",
    "licenseNote": "Terms are reproduced with attribution; consult original for full text and version history."
  },
  {
    "id": "iupac-periodic-table",
    "title": "IUPAC Periodic Table of Elements",
    "authors": [
      "IUPAC"
    ],
    "organization": "International Union of Pure and Applied Chemistry",
    "publisher": "IUPAC",
    "url": "https://iupac.org/what-we-do/periodic-table-of-elements/",
    "year": 2024,
    "accessedAt": "2026-08-21T00:00:00.000Z",
    "reviewedAt": "2026-08-22T00:00:00.000Z",
    "version": "2024 active",
    "sourceType": "iupac",
    "status": "active",
    "scopeNote": "Authoritative IUPAC periodic table: element names, symbols, group numbering 1-18, block assignment conventions, and placement guidance for group 3.",
    "licenseNote": "IUPAC material with attribution; check version date at source."
  },
  {
    "id": "ciaaw-atomic-weights-2021",
    "title": "CIAAW Standard Atomic Weights 2021",
    "authors": [
      "CIAAW",
      "IUPAC"
    ],
    "organization": "Commission on Isotopic Abundances and Atomic Weights (CIAAW) / IUPAC",
    "publisher": "CIAAW",
    "url": "https://ciaaw.org/atomic-weights.htm",
    "year": 2021,
    "updateYear": 2021,
    "accessedAt": "2026-08-21T00:00:00.000Z",
    "reviewedAt": "2026-08-22T00:00:00.000Z",
    "version": "2021",
    "sourceType": "ciaaw",
    "status": "active",
    "scopeNote": "Conventional/interval atomic weights for 118 elements. Supports displayed atomic weights, interval notation, and bracketed mass numbers in elements table and datasets.",
    "licenseNote": "Data used with attribution to CIAAW/IUPAC; values preserved as published."
  },
  {
    "id": "nist-atomic-weights",
    "title": "CIAAW Standard Atomic Weights 2021",
    "authors": [
      "CIAAW",
      "IUPAC"
    ],
    "organization": "Commission on Isotopic Abundances and Atomic Weights (CIAAW) / IUPAC",
    "publisher": "CIAAW",
    "url": "https://ciaaw.org/atomic-weights.htm",
    "year": 2021,
    "updateYear": 2021,
    "accessedAt": "2026-08-21T00:00:00.000Z",
    "reviewedAt": "2026-08-22T00:00:00.000Z",
    "version": "2021",
    "sourceType": "ciaaw",
    "status": "active",
    "scopeNote": "Conventional/interval atomic weights for 118 elements. Supports displayed atomic weights, interval notation, and bracketed mass numbers in elements table and datasets.",
    "licenseNote": "Data used with attribution to CIAAW/IUPAC; values preserved as published."
  },
  {
    "id": "nist-2022",
    "title": "NIST Chemistry WebBook — Thermochemical, Spectroscopic and Ion Energetics Reference Data",
    "authors": [
      "National Institute of Standards and Technology"
    ],
    "organization": "National Institute of Standards and Technology",
    "publisher": "NIST",
    "url": "https://webbook.nist.gov/chemistry/",
    "year": 2022,
    "accessedAt": "2026-08-21T00:00:00.000Z",
    "reviewedAt": "2026-08-22T00:00:00.000Z",
    "version": "WebBook active 2024",
    "sourceType": "nist",
    "status": "active",
    "scopeNote": "Evaluated thermochemistry, phase-change, vibrational, ion energetics and spectra. Used for reaction enthalpy, gas law, and property cross-checks.",
    "licenseNote": "U.S. government public domain; attribute NIST Chemistry WebBook."
  },
  {
    "id": "nist-constants-2022",
    "title": "CODATA Recommended Values of Fundamental Physical Constants: 2022",
    "authors": [
      "E. Tiesinga",
      "P. J. Mohr",
      "D. B. Newell",
      "B. N. Taylor"
    ],
    "organization": "National Institute of Standards and Technology",
    "publisher": "NIST",
    "url": "https://physics.nist.gov/cuu/Constants/",
    "doi": "10.1103/RevModPhys.93.025010",
    "year": 2022,
    "accessedAt": "2026-08-21T00:00:00.000Z",
    "reviewedAt": "2026-08-22T00:00:00.000Z",
    "version": "2022-CODATA",
    "sourceType": "nist",
    "status": "active",
    "scopeNote": "Definitive CODATA 2022 values for Avogadro constant, gas constant, Boltzmann, Planck, Faraday, etc. Used for calculator physics and formula pages.",
    "licenseNote": "Public domain U.S. government data; cite NIST CODATA 2022."
  },
  {
    "id": "nist-webbook",
    "title": "NIST Chemistry WebBook — Thermochemistry, Phase Change and Spectra",
    "authors": [
      "NIST"
    ],
    "organization": "National Institute of Standards and Technology",
    "publisher": "NIST",
    "url": "https://webbook.nist.gov/chemistry/",
    "year": 2024,
    "accessedAt": "2026-08-21T00:00:00.000Z",
    "reviewedAt": "2026-08-22T00:00:00.000Z",
    "version": "WebBook 2024",
    "sourceType": "nist",
    "status": "active",
    "scopeNote": "Evaluated constants and spectra; retained alongside nist-2022 as web entry point. Points to thermo and energetics collections.",
    "licenseNote": "U.S. government public domain."
  },
  {
    "id": "pubchem-periodic-table",
    "title": "PubChem Periodic Table and Element Data",
    "authors": [
      "National Center for Biotechnology Information"
    ],
    "organization": "National Library of Medicine / National Institutes of Health",
    "publisher": "PubChem",
    "url": "https://pubchem.ncbi.nlm.nih.gov/periodic-table/",
    "doi": "10.1093/nar/gkad408",
    "year": 2023,
    "accessedAt": "2026-08-21T00:00:00.000Z",
    "reviewedAt": "2026-08-22T00:00:00.000Z",
    "version": "PubChem 2023",
    "sourceType": "pubchem",
    "status": "active",
    "scopeNote": "Machine-readable element metadata, identifiers, and broad property summaries. Compound pages provide CID, CAS, and structural data with per-field citations.",
    "licenseNote": "PubChem data public domain with attribution."
  },
  {
    "id": "osha-chemical",
    "title": "Occupational Chemical Database and Safety & Health Regulations for Chemical Hazards",
    "authors": [
      "Occupational Safety and Health Administration"
    ],
    "organization": "U.S. Department of Labor — OSHA",
    "publisher": "OSHA",
    "url": "https://www.osha.gov/chemicaldata",
    "year": 2024,
    "accessedAt": "2026-08-21T00:00:00.000Z",
    "reviewedAt": "2026-08-22T00:00:00.000Z",
    "version": "OSHA 2024",
    "sourceType": "government",
    "status": "active",
    "scopeNote": "Workplace chemical exposure and SDS context for hazardous substances. Used for handling, ventilation, and disposal guidance language (not medical advice).",
    "licenseNote": "U.S. government public domain."
  },
  {
    "id": "acs-safety-ramp",
    "title": "Guidelines for Chemical Laboratory Safety in Secondary Schools & RAMP Framework",
    "authors": [
      "American Chemical Society"
    ],
    "organization": "American Chemical Society",
    "publisher": "ACS",
    "url": "https://www.acs.org/education/policies/middle-and-high-school-chemistry/safety.html",
    "year": 2024,
    "accessedAt": "2026-08-21T00:00:00.000Z",
    "reviewedAt": "2026-08-22T00:00:00.000Z",
    "version": "ACS 2024",
    "sourceType": "acs",
    "status": "active",
    "scopeNote": "Learner-facing safety pedagogy: Recognize, Assess, Minimize, Prepare for emergencies. Supports /safety and all experiment/lab callouts.",
    "licenseNote": "ACS educational material; cite and link to original."
  },
  {
    "id": "unece-ghs",
    "title": "Globally Harmonized System of Classification and Labelling of Chemicals (GHS), Rev. 11",
    "authors": [
      "UNECE"
    ],
    "organization": "United Nations Economic Commission for Europe",
    "publisher": "UNECE",
    "url": "https://unece.org/transport/dangerous-goods/ghs-rev11-2025",
    "year": 2025,
    "accessedAt": "2026-08-21T00:00:00.000Z",
    "reviewedAt": "2026-08-22T00:00:00.000Z",
    "version": "Rev. 11 (2025)",
    "sourceType": "ghs_sds",
    "status": "active",
    "scopeNote": "GHS hazard classes, signal words and pictograms. Referenced for label explanation, SDS orientation, and safety callouts.",
    "licenseNote": "UN publication; cite original."
  },
  {
    "id": "chang-gold",
    "title": "Chemistry",
    "authors": [
      "Raymond Chang",
      "Kenneth A. Goldsby"
    ],
    "publisher": "McGraw Hill",
    "url": "https://www.mheducation.com/",
    "isbn": "978-1-26-485430-8",
    "year": 2022,
    "accessedAt": "2026-08-21T00:00:00.000Z",
    "reviewedAt": "2026-08-22T00:00:00.000Z",
    "version": "13th ed. 2022",
    "sourceType": "textbook",
    "status": "active",
    "scopeNote": "General chemistry scope and pedagogy cross-check; not a substitute for primary IUPAC/NIST data. Used only where primary sources do not explain concept at learner level.",
    "licenseNote": "Copyrighted textbook; cite and reproduce only short, transformed explanations."
  },
  {
    "id": "tro-chemistry",
    "title": "Chemistry: Structure and Properties",
    "authors": [
      "Nivaldo J. Tro"
    ],
    "publisher": "Pearson",
    "url": "https://www.pearson.com/",
    "isbn": "978-0-13-752440-6",
    "year": 2023,
    "accessedAt": "2026-08-21T00:00:00.000Z",
    "reviewedAt": "2026-08-22T00:00:00.000Z",
    "version": "3rd ed. 2023",
    "sourceType": "textbook",
    "status": "active",
    "scopeNote": "Pedagogy and concept scope cross-check for introductory college level; primary numeric data remains IUPAC/NIST.",
    "licenseNote": "Copyrighted; use for scope reference, not verbatim copying."
  },
  {
    "id": "openstax-chemistry-2e",
    "title": "Chemistry 2e — Scope Cross-Check Only",
    "authors": [
      "Paul Flowers",
      "Klaus Theopold",
      "Richard Langley",
      "William R. Robinson"
    ],
    "organization": "OpenStax / Rice University",
    "publisher": "OpenStax",
    "url": "https://openstax.org/details/books/chemistry-2e",
    "year": 2019,
    "accessedAt": "2026-08-21T00:00:00.000Z",
    "reviewedAt": "2026-08-22T00:00:00.000Z",
    "version": "2e (2019)",
    "sourceType": "oer",
    "status": "active",
    "scopeNote": "Open educational resource used solely for scope and sequence cross-check; never as primary for numeric data or safety.",
    "licenseNote": "CC BY 4.0; attribute OpenStax."
  }
]

How content cites sources

Lessons, topics, formulas, glossary, and blog set referenceIds to one or more source IDs above; the UI renders them via SourceList with the same IDs.
Datasets (src/data/elements.ts, compounds.ts, reactions.ts) list sources: string[] per record; property-level provenance carries pinpoint and last-verified date where needed.
Calculators cite physics in Assumptions and in code comments (src/lib/chemistry/calculators/*).

Change notes and last-reviewed semantics

`lastReviewedAt` marks a real editorial/chemistry review, not a routine deployment. Substantive scientific updates receive a correction/change note in /corrections. Trivial code or style deploys do not advance review dates.

Last reviewed: 2026-08-23 · Maintainer: Chemistry Fundamentals Editorial Team · Report an error: /corrections · Contact

CORE TOPICS

LEARNING PATHS

QUICK RESOURCES

TOOLS

PRACTICE

REFERENCE