Element 26 · Transition metal
Iron (Fe) — Element 26
Anglo-Saxon iren
Iron (Fe) is a transition metal in Period 4, Group 8 of the periodic table with atomic number 26, standard atomic weight 55.845 u, and ground-state electron configuration [Ar] 3d⁶ 4s². At standard temperature and pressure it is classified as a solid with 8 valence electrons and common oxidation states +2, +3.
Steel, hemoglobin, Earth's core
What are the atomic properties and physical constants of Iron?
Reference constants compiled from IUPAC standard atomic weights, the NIST Atomic Spectra Database, and the CRC Handbook.
- Atomic number (Z)
- 26
- Standard atomic mass
- 55.845 u
- Chemical family
- Transition metal
- Ground-state configuration
- [Ar] 3d⁶ 4s²
- Electrons per shell
- 2, 8, 14, 2
- Valence electrons
- 8
- Common ion charges / oxidation states
- +2, +3
- Phase at STP
- Solid
- Pauling electronegativity
- 1.83 Pauling
- First ionization energy
- 762 kJ/mol
- Atomic radius
- 156 pm
- Melting point
- 1,538 °C
- Boiling point
- 2,862 °C
- Discovery year
- Ancient
- Table coordinate
- Period 4, Group 8
- Radioactivity
- Has stable isotope(s)
How are electrons arranged across Iron’s shells?
A neutral Iron atom contains 26 electrons distributed across 4 occupied principal energy shells ([Ar] 3d⁶ 4s²). The table below compares Iron’s shell occupancy against each shell’s theoretical 2n² capacity.
| Principal Shell (n) | Spectroscopic Letter | Electrons in Fe | Max Shell Capacity (2n²) |
|---|---|---|---|
| n = 1 | K | 2 e⁻ | 2 e⁻ |
| n = 2 | L | 8 e⁻ | 8 e⁻ |
| n = 3 | M | 14 e⁻ | 18 e⁻ |
| n = 4 | N | 2 e⁻ | 32 e⁻ |
Frequently Asked Questions about Iron (Fe)
What is the atomic mass and atomic number of Iron (Fe)?
Iron (Fe) has atomic number Z = 26 (26 protons in its nucleus) and an IUPAC standard atomic weight of 55.845 u. It sits in Period 4, Group 8 and is classified as a transition metal.
What is the ground-state electron configuration of Iron?
The neutral ground-state electron configuration of Iron (Z = 26) is [Ar] 3d⁶ 4s². Across its 4 occupied principal shells (n = 1 to n = 4), the electrons per shell are 2, 8, 14, 2, with 8 valence electrons participating in bonding.
What are the common ion charges and electronegativity of Iron?
Iron commonly forms +2, +3 oxidation states or ion charges in compounds. Its Pauling electronegativity is 1.83 and its first ionization energy is 762 kJ/mol.
When was Iron discovered and what is it used for?
Iron was discovered in Ancient (Anglo-Saxon iren). Steel, hemoglobin, Earth's core
How does Iron compare to neighboring elements?
Other transition metal elements: