#26 / 118
26Fe55.845
Transition Metalssolid at STPD-block

Iron

Group: 8Period: 4Standard Atomic Weight: 55.845 u

Why is Iron in this position?

Understanding the scientific rationale behind Iron's position in the periodic table:

Group Assignment
Group 8

Belongs to Group 8 because it has 8 valence electrons (3d⁶ 4s²).

Period Assignment
Period 4

Belongs to Period 4 because its outermost electrons occupy n=4.

Orbital Block
D-block

Belongs to the d-block because its differentiating electrons enter 3d orbitals.

Chemical Category
Transition Metals

Classified as a transition metal with hallmark ferromagnetism and catalytic properties.

Atomic Structure & Bohr Shell Model

Shell Distribution: [2, 8, 14, 2]

Bohr Atomic Shell Model(2, 8, 14, 2)

Hover or tap any shell orbit ring to inspect electron counts and 2n² capacities.

26 Protons (p⁺)30 Neutrons (n⁰)
KShell K: Electron 1 of 2Shell K: Electron 2 of 2LShell L: Electron 1 of 8Shell L: Electron 2 of 8Shell L: Electron 3 of 8Shell L: Electron 4 of 8Shell L: Electron 5 of 8Shell L: Electron 6 of 8Shell L: Electron 7 of 8Shell L: Electron 8 of 8MShell M: Electron 1 of 14Shell M: Electron 2 of 14Shell M: Electron 3 of 14Shell M: Electron 4 of 14Shell M: Electron 5 of 14Shell M: Electron 6 of 14Shell M: Electron 7 of 14Shell M: Electron 8 of 14Shell M: Electron 9 of 14Shell M: Electron 10 of 14Shell M: Electron 11 of 14Shell M: Electron 12 of 14Shell M: Electron 13 of 14Shell M: Electron 14 of 14NShell N: Electron 1 of 2Shell N: Electron 2 of 2FeZ = 26

Educational Note: This Niels Bohr planetary model visually illustrates principal quantum energy shells ($n=1, 2, 3\dots$) and electron counts. In modern quantum mechanics (Schrödinger model), electrons do not orbit in fixed circular planetary tracks, but exist as 3D probability clouds (orbitals: $s, p, d, f$) governed by the Heisenberg uncertainty principle.

Electron Shell Filling Breakdown

Shell K (n=1):2 / 2 electrons (100%)
Shell L (n=2):8 / 8 electrons (100%)
Shell M (n=3):14 / 18 electrons (78%)
Shell N (n=4):2 / 32 electrons (6%)
Aufbau Electron Configuration
1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s²

Neutral ground state configuration. Valence electrons: 8.

Atomic & Quantum Properties

Electronegativity (Pauling)1.83 Pauling
1st Ionization Energy762.5 kJ/mol
Electron Affinity-15.7 kJ/mol
Atomic Radius (empirical)156 pm
Common Oxidation States+2, +3
Crystal StructureBCC / FCC

Physical & Thermal Properties

Density at STP7.87 g/cm³
Melting Point1538 °C (1811 K)
Boiling Point2862 °C (3135 K)
Magnetic OrderingFerromagnetic
Discovery YearAncient
Discovered ByKnown since prehistoric times (Iron Age)

Real-World Uses, Occurrence & Compounds

Major Industrial & Everyday Uses
  • Structural steel and cast iron for bridges, buildings, railways, and ships
  • Automotive chassis, engines, and heavy industrial machinery
  • Biological oxygen transport in vertebrate blood (hemoglobin)
  • Industrial catalysts for the Haber ammonia synthesis process
Occurrence in Nature

Fourth most abundant element in Earth's crust (5.6%) and the primary constituent of Earth's outer and inner liquid/solid core; mined as hematite (Fe₂O₃) and magnetite (Fe₃O₄).

Etymology & Name Origin

From Proto-Germanic 'isarnan'; symbol Fe from Latin 'ferrum'

Important Chemical Compounds
Fe₂O₃ (Hematite / Rust)
Fe₃O₄ (Magnetite)
FeSO₄ (Ferrous sulfate)
FeCl₃ (Ferric chloride)
Interesting Chemical Facts
  • Iron-56 has one of the highest nuclear binding energies per nucleon in physics, marking the end of energy-yielding stellar nuclear fusion in massive stars.
  • Earth's molten iron-nickel outer core functions as a geodynamo, generating the protective geomagnetic field shielding Earth from solar wind.
  • Mars appears distinctly red across the night sky because its surface is blanketed in rusty iron(III) oxide dust.
Safety & Handling Note

Elemental iron is generally non-toxic and essential for human life, but iron overdose is a leading cause of accidental poisoning in young children.