Iron
Iron is the most widely used metal in the modern world, the backbone of steel and countless machines, buildings, and vehicles. Humans have worked with it for thousands of years, long before anyone understood what an element even was, and it's just as essential inside the body, where it lets red blood cells carry oxygen.
- Group · Period
- 8 · 4
- At room temp
- solid
- Melts at
- 1811 K
- Density
- 7.874 g/cm³
- Discovered
- Ancient
Uses
Iron’s overwhelming use today is as the base metal for steel, an alloy of iron with carbon and often other elements that underpins construction, transportation, and manufacturing worldwide — from skyscraper frames and bridges to cars, ships, and machine tools. Cast iron and various iron alloys also show up in everything from cookware to engine blocks, valued for their strength and relatively low cost compared with other structural metals.
Iron is just as essential inside living things: it’s the core of hemoglobin, the molecule in red blood cells that binds oxygen in the lungs and releases it throughout the body, making dietary iron a necessary part of human nutrition.
History
Iron has no single discoverer — humans have worked with it since prehistoric times, initially using rare pieces of meteoric iron and later learning to smelt it from ore, a technology that spread and developed independently across multiple ancient civilizations. Its adoption for tools and weapons was significant enough to mark an entire period of human history, the Iron Age, as it gradually displaced the bronze that earlier societies had relied on. Because it predates written chemistry entirely, iron’s “discovery” is really a long, gradual story of metallurgical skill rather than a single event.
Fun facts
- Iron is believed to make up most of the mass of Earth's core, making it the most abundant element on the planet as a whole, even though it's not the most common in the crust.
- The transition from bronze to iron tools and weapons was significant enough to give an entire era of human history its name — the Iron Age.
- Hemoglobin, the protein that carries oxygen in red blood cells, relies on iron atoms to bind and release oxygen as blood circulates through the body.
Frequently asked questions
Who discovered iron?
No one person discovered it — iron has been worked by humans since prehistoric times, first from rare meteoric iron and later from smelted ore, with different cultures developing ironworking independently. Because it was known and used long before the idea of chemical elements existed, there's no single discovery story the way there is for elements found in a laboratory.
Why does iron rust, and why is that a problem?
Iron reacts with oxygen and moisture in the air to form iron oxide, which is what we call rust. Unlike the protective oxide layer that forms on metals like chromium or aluminum, rust is flaky and doesn't stick well, so it keeps flaking off and exposing fresh metal underneath — which is why untreated iron and steel structures gradually corrode away if left exposed.
Is the iron in food the same as the iron in steel?
It's the same element, but in completely different forms. Steel is mostly metallic iron alloyed with carbon and other elements, while dietary iron comes bound up in compounds the body can absorb and use to build hemoglobin. You couldn't get nutritional value from eating a nail, since the body can't break down and absorb metallic iron the way it can iron from food.
Compounds
2 notable compounds containing Fe
- Fe2O3oxide
Iron(III) oxide
A reddish-brown ionic oxide that forms when iron corrodes in the presence of oxygen and moisture, commonly known as rust.
Used for: Pigment in paints, polishing compound, iron ore for steelmaking
- Nd2Fe14Bindustrial
Neodymium iron boron
An intermetallic compound whose tetragonal crystal structure produces the strongest permanent magnets commercially available, far outperforming older ferrite and alnico magnets.
Used for: Permanent magnets in electric motors, headphones, and hard drives
Isotopes
32 known isotopes
Swipe to see all columns →
| Isotope | Natural abundance | Half-life | Decay mode | Mass excess | Binding energy / nucleon | Decay width |
|---|---|---|---|---|---|---|
| Fe-54 stable | 5.845% | Stable | — | -56,254.62 keV | 8,736.38 keV | — |
| Fe-56 stable | 91.754% | Stable | — | -60,607.16 keV | 8,790.36 keV | — |
| Fe-57 stable | 2.119% | Stable | — | -60,182.02 keV | 8,770.28 keV | — |
| Fe-58 stable | 0.282% | Stable | — | -62,155.27 keV | 8,792.25 keV | — |
Show all 32 isotopes
| Fe-45 | — | 1.89 ms | Two-proton emission (57%), Electron capture / beta-plus decay (43%), Beta-plus, proton emission (43%) | 14,408 keV | 7,299 keV | 2.41 × 10-13 eV |
| Fe-46 | — | 13.0 ms | Electron capture / beta-plus decay (100%), ECP (78.7%) | 1,210 keV | 7,603 keV | 3.51 × 10-14 eV |
| Fe-47 | — | 21.8 ms | Electron capture / beta-plus decay (100%), ECP (0%), EC2P | -7,130 keV | 7,790 keV | 2.09 × 10-14 eV |
| Fe-48 | — | 45.5 ms | Electron capture / beta-plus decay (100%), ECP (15.3%) | -18,008.58 keV | 8,022.73 keV | 1.00 × 10-14 eV |
| Fe-49 | — | 64.7 ms | Electron capture / beta-plus decay (100%), Beta-plus, proton emission (56.7%) | -24,750.73 keV | 8,161.31 keV | 7.05 × 10-15 eV |
| Fe-50 | — | 152.0 ms | Electron capture / beta-plus decay (100%), ECP (0%) | -34,476.46 keV | 8,354.03 keV | 3.00 × 10-15 eV |
| Fe-51 | — | 305 ms | Electron capture / beta-plus decay (100%) | -40,189.19 keV | 8,460.5 keV | 1.50 × 10-15 eV |
| Fe-52 | — | 8.275 h | Electron capture / beta-plus decay (100%) | -48,332.1 keV | 8,609.61 keV | 1.53 × 10-20 eV |
| Fe-53 | — | 8.51 m | Electron capture / beta-plus decay (100%) | -50,947.48 keV | 8,648.8 keV | 8.94 × 10-19 eV |
| Fe-55 | — | 2.744 Y | Electron capture (100%) | -57,481.42 keV | 8,746.6 keV | 5.27 × 10-24 eV |
| Fe-59 | — | 44.490 d | Beta-minus decay (100%) | -60,664.96 keV | 8,754.77 keV | 1.19 × 10-22 eV |
| Fe-60 | — | 2.62E+6 Y | Beta-minus decay (100%) | -61,413.17 keV | 8,755.85 keV | 5.52 × 10-30 eV |
| Fe-61 | — | 5.98 m | Beta-minus decay (100%) | -58,920.5 keV | 8,703.77 keV | 1.27 × 10-18 eV |
| Fe-62 | — | 68 s | Beta-minus decay (100%) | -58,878.06 keV | 8,692.88 keV | 6.71 × 10-18 eV |
| Fe-63 | — | 6.1 s | Beta-minus decay (100%) | -55,635.63 keV | 8,631.55 keV | 7.48 × 10-17 eV |
| Fe-64 | — | 2.0 s | Beta-minus decay (100%) | -54,969.55 keV | 8,612.39 keV | 2.28 × 10-16 eV |
| Fe-65 | — | 0.81 s | Beta-minus decay (100%) | -51,217.9 keV | 8,546.35 keV | 5.63 × 10-16 eV |
| Fe-66 | — | 440 ms | Beta-minus decay (100%) | -50,067.85 keV | 8,521.72 keV | 1.04 × 10-15 eV |
| Fe-67 | — | 0.6 s | Beta-minus decay (100%) | -45,708.42 keV | 8,449.94 keV | 7.60 × 10-16 eV |
| Fe-68 | — | 188 ms | Beta-minus decay (100%), Beta-minus, neutron emission (0%) | -43,897 keV | 8,418 keV | 2.43 × 10-15 eV |
| Fe-69 | — | 110 ms | Beta-minus decay (100%) | -39,199 keV | 8,345 keV | 4.15 × 10-15 eV |
| Fe-70 | — | 65 ms | Beta-minus decay (100%), Beta-minus, neutron emission | -36,890 keV | 8,308 keV | 7.02 × 10-15 eV |
| Fe-71 | — | 35.7 ms | Beta-minus decay (100%), B-2N, Beta-minus, neutron emission | -31,930 keV | 8,235 keV | 1.28 × 10-14 eV |
| Fe-72 | — | 150 ns | Beta-minus decay (100%), Beta-minus, neutron emission (27.6%) | -29,250 keV | 8,195 keV | 3.04 × 10-9 eV |
| Fe-73 | — | 12.9 ms | Beta-minus decay (100%), Beta-minus, neutron emission, B-2N | -23,990 keV | 8,121 keV | 3.54 × 10-14 eV |
| Fe-74 | — | 8.2 ms | B-2N, Beta-minus, neutron emission, Beta-minus decay | -20,660 keV | 8,076 keV | 5.56 × 10-14 eV |
| Fe-75 | — | 620 ns | Beta-minus decay, Beta-minus, neutron emission, B-2N | -14,700 keV | 7,996 keV | 7.36 × 10-10 eV |
| Fe-76 | — | — | Beta-minus decay (100%), B-2N, B-3N | -10,590 keV | 7,943 keV | — |