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Iron(III) ion

Fe3+Fe^{3+}

Charge: 3+ · Type: Cation · Molar mass: 55.845 g/mol

Made of: iron

How it forms

Fe3+ forms when iron loses its two 4s electrons and one 3d electron, leaving a half-filled 3d subshell that is relatively stable. Iron(II) compounds oxidize to iron(III) in air, which is why fresh iron(II) solutions darken over time.

Naming note

Fe3+ is named iron(III); the older name is ferric ion. The Roman numeral distinguishes it from iron(II).

Examples in compounds

  • Iron(III) oxide

  • Iron(III) chloride

  • Iron(III) nitrate

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