Recognised as Chemical element
Iron
- Fe
- Z = 26
- transition metal
Iron (Fe) is element 26, a transition metal in period 4 and group 8. Its standard atomic weight is 55.845 Da. Weights follow IUPAC standard atomic weights, 2021 revision.
Identity
SymbolFe
Standard atomic weight55.845atomic mass units (Da)
Mass in kilograms9.2732804 × 10^-26
Categorytransition metal
Group8
Period4
Blockd-block
Electrons in a neutral atom26
Neutrons in the most common isotope30≈
Electron configuration
Configuration1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s²ground state, subshells written in order of n
Noble gas shorthand[Ar] 3d⁶ 4s²
Electrons per shell2, 8, 14, 2K, L, M and outward
Electrons in the outer shell2
Unpaired electrons4Hund's rule; unpaired electrons make the free atom paramagnetic
Madelung ruleFollowedthe ground state is what the n + l filling order predicts
Quantities
Molar mass55.845 g/mol
Mass of one mole55.845 grams
Atoms in one gram1.078367 × 10^22
Mass of one atom9.2732804 × 10^-23 g
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