Iron (Fe): electron configuration, atomic mass and facts
Iron (Fe) is element 26 of the periodic table, a transition metal in period 4, group 8. Its electron configuration is [Ar] 3d6 4s2, with electrons arranged in shells 2, 8, 14, 2, and its standard atomic weight is 55.845 u.
💡 The most used metal on Earth. The planet’s core is mostly iron.
▶ Watch Iron’s electrons orbit in the interactive periodic tableIron at a glance
| Symbol | Fe |
|---|---|
| Atomic number | 26 |
| Atomic mass | 55.845 u |
| Category | Transition metal |
| Group | 8 |
| Period | 4 |
| Block | d-block |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 3d6 4s2 |
| Noble-gas shorthand | [Ar] 3d6 4s2 |
| Electrons per shell | 2, 8, 14, 2 |
| Electronegativity (Pauling) | 1.83 |
| State at 20 °C | solid |
Experiments with iron
🔩 Iron nail in copper sulfate
A more reactive metal displaces copper: the nail turns pink and the blue fades to green.
🩸 Fe³⁺ thiocyanate test
A drop of thiocyanate turns iron(III) solutions blood red.
☄️ Thermite
Aluminium reduces iron oxide in a shower of sparks and molten iron.
Where is Iron on the periodic table?
Iron is in period 4, group 8, in the d-block. The period number matches its 4 electron shells, and the block names the subshell its last electrons fill. In the same group, Ruthenium sits directly below it. Elements in the same column of the d-block often have similar chemistry.
How to work out the electron configuration of Iron
Put 26 electrons into subshells in order of rising energy, filling each before starting the next: 1s² (2), 2s² (4), 2p⁶ (10), 3s² (12), 3p⁶ (18), 4s² (20), 3d⁶ (26). In shorthand, [Ar] stands for the 18 electrons of argon, giving [Ar] 3d⁶ 4s².
How electronegative is Iron?
Iron has a Pauling electronegativity of 1.83, ranking 42 of the 100 elements with a known value (fluorine is highest at 3.98). That is in the middle of the range.
Iron in the virtual lab
Faradium’s chemistry workbench includes these chemicals that contain iron: Iron nail / filings, Iron(II) sulfate crystals, Iron(III) oxide, Iron(III) chloride, Iron(II) sulfate. Open the Chemistry Lab to experiment with them.
Frequently asked questions
What is the electron configuration of Iron?
The electron configuration of Iron (Fe) is 1s2 2s2 2p6 3s2 3p6 3d6 4s2. In noble-gas shorthand it is written [Ar] 3d6 4s2.
How many electrons does Iron have in each shell?
Iron has 26 electrons arranged in shells as 2, 8, 14, 2.
What is the atomic mass of Iron?
The standard atomic weight of Iron is 55.845 u, so one mole of Iron atoms has a mass of about 55.845 g.
Is Iron a metal?
Yes. Iron is a transition metal.
Explore nearby elements
More transition metals: Vanadium, Chromium, Manganese, Cobalt, Nickel, Copper. See all elements on the periodic table.