Iron (Fe)
Iron is the 26th element, a transition metal in the d-block. Its standard atomic weight is 55.845.
Iron
55.845
What the table records
- Atomic number
- 26
- Standard atomic weight
- 55.845
- Group
- 8
- Period
- 4
- Block
- d-block
- Category
- Transition metal
- [Ar] 3d6 4s2
- Valence electrons
- 8
- Typical valence
- Van der Waals radius
- 2.05 Å
- Covalent radius
- 1.32 Å
Molecules containing iron
The lightest named structures in this library that contain Fe.
Ferric cation
Fe+3 · 55.85 g/mol
Ferrous cation
Fe+2 · 55.85 g/mol
Iron
Fe · 55.85 g/mol
Iron oxide (Fe2O3)
Fe₂O₃ · 159.69 g/mol
Iron chloride (FeCl3)
Cl₃Fe · 162.2 g/mol
Ferrocene
C₁₀H₁₀Fe · 186.04 g/mol
Ferric acetylacetonate
C₁₅H₂₁FeO₆ · 353.17 g/mol
1,1′-Bis(diisopropylphosphino)ferrocene
C₂₂H₃₆FeP₂ · 418.32 g/mol
1,1'-Bis[bis(1,1-dimethylethyl)phosphino]ferrocene
C₂₆H₄₄FeP₂ · 474.43 g/mol
C26H44FeP2
C₂₆H₄₄FeP₂ · 474.43 g/mol
1,1'-Bis(diphenylphosphino)ferrocene
C₃₄H₂₈FeP₂ · 554.39 g/mol
1,1'-Ferrocenediyl-bis(diphenylphosphine)
C₃₄H₂₈FeP₂ · 554.39 g/mol
How to read these numbers
The standard atomic weight is an average over the isotopes as they occur naturally, which is why it is rarely a whole number. It is the figure a molar mass calculation uses. Work in mass spectrometry wants the monoisotopic mass of a single isotope instead, which is a different number.
The two radii are not the same measurement. The covalent radius is half the distance between two bonded atoms of the element; the van der Waals radius is how close a non-bonded atom gets before repulsion takes over, and is always the larger. Space-filling models are drawn with the second, ball-and-stick models with the first — which is why the same molecule looks so different in the two.