Binary‑Ionic Rules & Examples (“Chem Nomenclature – Binary Ionic”)

Term

Definition

Fixed‑charge metal rule

Metal name + non‑metal stem + “‑ide” (e.g. NaCl → sodium chloride)

Variable‑charge metal rule

Include Roman numeral in name (e.g. FeCl3 → iron(III) chloride)

“Swap & Drop” steps

1) Write ions 2) Criss‑cross charges 3) Reduce subscripts

What needs Roman numerals?

Transition metals with variable charge (Fe

NaBr → ?

sodium bromide

MgO → ?

magnesium oxide

Cu2O → ?

copper(I) oxide

iron(III) oxide → ?

Fe2O3

tin(II) chloride → ?

SnCl2

Ca3N2 → ?

calcium nitride

Al2S3 → ?

aluminum sulfide

chromium(III) iodide → ?

CrI3

K2S → ?

potassium sulfide

silver sulfide → ?

Ag2S

zinc phosphate → ?

Zn3(PO4)2

Scandium oxide → ?

Sc2O3

Lead(IV) oxide → ?

PbO2

Common fixed‑charge metals list

Ag⁺ Zn²⁺ Cd²⁺ Al³⁺ Sc³⁺

Need‑to‑know ions for names

oxide O²⁻; sulfide S²⁻; nitride N³⁻; phosphide P³⁻; chloride Cl⁻

Polyatomic rule

Keep ion name unchanged (e.g. NaNO3 → sodium nitrate)