Iron (Fe)
Element 26 · Transition metal · atomic mass 55.845 u · group 8, period 4
Electron shells: 2, 8, 14, 2
Iron is the most-used metal on Earth and the heaviest element that stars can fuse while still releasing energy. Its compound haemoglobin carries oxygen through your blood.
Earth's core is mostly iron — and its churning is what gives us a magnetic field.
- Atomic number
- 26
- Atomic mass
- 55.845 u
- Electron configuration
- [Ar] 4s² 3d⁶
- Group · period · block
- 8 · 4 · d
- Oxidation states
- +2, +3
- Electronegativity
- 1.83 (Pauling)
- Melting point
- 1,538 °C
- Boiling point
- 2,861 °C
- Density
- 7.874 g/cm³
- State at 20 °C
- Solid
- Appearance
- Lustrous grey metal
- Discovered
- Known since antiquity
26 protons, and 26 electrons when neutral
IUPAC standard atomic weight
Iron group
What Iron is used for
- Steel for construction and vehicles
- Cast-iron machinery and cookware
- Magnets and transformer cores
- Catalyst for ammonia synthesis
Atomic structure of Iron
A neutral iron atom has 26 protons and 26 electrons. Its most common isotope carries about 30 neutrons, which is where the mass number 56 comes from. Change the neutron count and you have a different isotope of iron; change the proton count and you have a different element entirely.
Those electrons fill shells from the inside out: 2, 8, 14, 2. In orbital notation that is [Ar] 4s² 3d⁶. As a d-block element its valence count is variable, which is why it can form compounds in several oxidation states.
3D electron orbitals
See where Iron's electrons actually are — a cloud of 26,000 points sampled from the probability density |ψ|², not a cartoon of a lobe.
Where Iron sits in the periodic table
Discovery and naming
Iron has been known and used since antiquity, long before anyone could describe it as an element. Its name comes from Old English iren; symbol from Latin ferrum, which is also why its symbol (Fe) does not match its English name.
Keep exploring
Atomic weight from IUPAC/CIAAW; physical properties from PubChem (US National Library of Medicine). Values that have never been measured are shown as “not measured” rather than estimated.
Related Calculators
Frequently Asked Questions
What is the atomic mass of Iron?
The standard atomic weight of Iron is 55.845 u, as published by IUPAC's Commission on Isotopic Abundances and Atomic Weights.
How many protons, neutrons and electrons does Iron have?
Iron has 26 protons, because the atomic number is the proton count and that is what makes an atom Iron at all. A neutral Iron atom has the same number of electrons, 26. The neutron count varies by isotope; the most common one has about 30, since 56 − 26 = 30.
What is the electron configuration of Iron?
The electron configuration of Iron is [Ar] 4s² 3d⁶. Its electrons are arranged 2, 8, 14, 2 across 4 shells.
Is Iron a metal?
Yes. Iron is classified as a transition metal, on the metallic side of the table.
What group and period is Iron in?
Iron is in group 8 (the iron group), period 4, in the d-block. The group is its column and the period is its row.
What is the charge of Iron?
Iron most commonly forms a 2+ or 3+ ion. Like most transition metals it has several accessible oxidation states, so the charge depends on the compound.
What is the melting point of Iron?
Iron melts at 1,538 °C and boils at 2,861 °C. That puts it in the solids at everyday temperatures.
What is Iron used for?
Steel for construction and vehicles, Cast-iron machinery and cookware, Magnets and transformer cores, Catalyst for ammonia synthesis. Iron is the most-used metal on Earth and the heaviest element that stars can fuse while still releasing energy.
Who discovered Iron, and where does its name come from?
Iron (Fe) has been known and used since antiquity, long before anyone could describe it as an element. The name comes from Old English iren; symbol from Latin ferrum.