Iron commonly forms Fe2+ Fe3+ in introductory ionic compounds.
| Element | Iron |
|---|---|
| Symbol | Fe |
| Atomic number | 26 |
| Common ionic charge | +2, +3 |
| Common ions | Fe2+, Fe3+ |
Images are used as visual references; charge rules still depend on the compound.
Iron is [Ar]3d6 4s2. Dropping the two 4s electrons gives Fe2+; dropping one d electron more reaches Fe3+, whose half-filled d5 configuration is unusually stable. The two states sit close in energy, so iron flips between them constantly — the basis of rusting and of respiration alike.
This is a classroom reference range, not an exhaustive list of all oxidation states.
Writing iron oxide as FeO whenever the problem says 'iron oxide.' There are two: FeO (iron(II)) and Fe2O3 (iron(III), the red one). If the name lacks a numeral, look at context — rust, ore, and most pigments are the +3 version.
Ferrous = Fe2+, so ferrous sulfate is FeSO4 (one 2+ cancels one sulfate 2-). Ferritin stores iron as Fe3+; your gut absorbs iron best as Fe2+, which is why supplements use the ferrous form.
Iron chloride
Fe2+ balances chloride ions.
Iron oxide
Iron can form oxides where total positive and negative charge balances.
Oxygen and water team up to strip electrons: Fe → Fe2+ → Fe3+, ending as hydrated Fe2O3. Each step is a small electrochemical cell on the metal's surface — which is why salt water (a better electrolyte) rusts cars faster.
Magnetite is a mixed-charge compound: one Fe2+ and two Fe3+ per formula unit (2 + 3 + 3 = 8 = four O2-). Many transition metals form such mixed-valence oxides; magnetite's electron-hopping between the two states makes it conduct and magnetize.
Alphabetical and numerical order match: ferrOUS before ferrIC, 2 before 3. Or note that 'ic' = 'I count higher.'
Combine positive and negative ions so the total charge is zero — or let the ionic compound calculator do the crossing for you. The full chart lives on the periodic table with charges.
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