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.
NOT BSTOTAL BS
SOME BS — Verdict: Mixed
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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.