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Many inorganic binary formulas list the more electropositive element first.

The Claim

When writing a chemical formula, the core rule for deciding element order is to write the more electropositive (lower electronegativity) element first and the more electronegative element last.

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The Short Version

The statement captures an important convention, but it overstates its scope. Electropositive-first ordering is widely used for many inorganic binary formulas, yet IUPAC does not treat it as the universal rule for chemical formulas overall. Organic and many molecular formulas commonly follow Hill notation, and some inorganic cases use other conventions or established traditional order.

Caveats

  • The rule applies mainly to many inorganic binary compounds, not to all chemical formulas.
  • Hill notation is a major standard for molecular and organic formulas: C first, H second, then the rest alphabetically.
  • Established usage and special conventions can override electronegativity order, so treating it as a universal deciding rule is inaccurate.

The Receipts

  1. IUPAC Provisional Recommendations – Nomenclature of Inorganic Chemistry (excerpt, IR-4.3.4, IR-4.4)

    IUPAC

  2. Brief Guide to Nomenclature of Inorganic Chemistry

    IUPAC/Queen Mary University of London

  3. Nomenclature of Inorganic Chemistry: IUPAC Recommendations 2005

    IUPAC

  4. Hill notation

    IUPAC Gold Book

  5. Inorganic compound (IUPAC Compendium of Chemical Terminology)

    IUPAC Gold Book

  6. inorganic compound

    IUPAC Gold Book

  7. Representation of chemical structures in PubChem

    PubChem (NIH/NLM)

  8. What Is a Chemical Formula?

    American Chemical Society

  9. 5.8: Naming Molecular Compounds

    Chemistry LibreTexts

  10. Compounds and chemical formulas

    Khan Academy

+ 8 more sources — see the full list on Lenz

Filed Under

Hill SystemInternational Union Of Pure And Applied Chemistry

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