Iron
Iron (Fe, atomic number 26) is a Period 4 transition metal (d-block, 55.845 u). Endpoint of exothermic stellar fusion in massive stars and dominant constituent of Earth's liquid outer and solid inner core (generating the geomagnetic dynamo). Coordina
Iron is a chemical element on the periodic table with the atomic symbol Fe, atomic number 26, and standard atomic weight 55.845 u. Classified as a Transition Metal within Group 8 and Period 4 (d-block), iron possesses a ground-state electron configuration of [Ar] 3d6 4s2 distributed across 4 concentric Bohr electron shells (2 · 8 · 14 · 2) with 2 outer-shell electrons. Endpoint of exothermic stellar fusion in massive stars and dominant constituent of Earth's liquid outer and solid inner core (generating the geomagnetic dynamo). Coordinates O₂ in hemoglobin and transfers electrons in cytochromes.
⚛️ Interactive Periodic Table Lab: Explore Iron (Fe, Z = 26) in the CRV Science Dynamic Periodic Table & Bohr Orbital Lab to visualize its animated 2 · 8 · 14 · 2 electron shells, simulate live phase transitions from 0 K to 6,000 K, and compare periodic heatmaps across all 118 IUPAC elements.
Atomic Structure and Periodic Trends: How Do Quantum Orbitals Define Iron?
Electron Shell Architecture and Ground-State Configuration
A neutral atom of iron contains 26 protons in its atomic nucleus balanced by 26 electrons occupying quantized atomic orbitals. In the Bohr-Sommerfeld and quantum-mechanical orbital models, these electrons populate 4 principal energy shells (K (n=1): 2e−, L (n=2): 8e−, M (n=3): 14e−, N (n=4): 2e−), terminating in the four-lobed d-orbital manifold (azimuthal quantum number l = 2) with ground-state configuration [Ar] 3d6 4s2. Removing the most loosely bound valence electron from an isolated gaseous iron atom requires a first ionization energy of 762 kJ/mol, while its tendency to attract shared bonding electrons is quantified by a Pauling electronegativity of 1.83.
Periodic Table Position and Neighboring Elements
Within the periodic table, Iron occupies Period 4, Group 8 of the d-block (Transition Metals). Along Period 4, it is flanked by Manganese (Mn, Z = 25) and Cobalt (Co, Z = 27). Vertically within its periodic family, Iron shares valence orbital symmetry and homologous chemical trends with Ruthenium (Ru), Osmium (Os), Hassium (Hs). Learners can interactively compare Iron's orbital radii, ionization energy, and Pauling electronegativity against all neighboring elements in the Dynamic Periodic Table Lab.
Physical and Thermodynamic Properties: How Does Iron Behave Across Temperature Regimes?
Standard Phase, Melting Point, and Boiling Point Dynamics
At standard ambient temperature and pressure (298.15 K / 25 °C, 1 atm), elemental iron exists as a crystalline solid. As thermal energy increases, its crystal or molecular lattice undergoes solid-to-liquid fusion at a melting point of 1,811 K (+1537.85 °C / +2800.1 °F) and transitions to the vapor phase at a normal boiling point of 3,134 K (+2860.85 °C / +5181.5 °F), spanning a liquid thermodynamic range of 1323 K. In the CRV Science Dynamic Periodic Table, dragging the live temperature slider between absolute zero (0 K) and solar-photosphere temperatures (6,000 K) dynamically tracks Iron's state transitions in real time alongside enthalpy and entropy phase equilibria.
Quantitative Atomic and Thermodynamic Parameter Matrix
| Parameter | Quantitative Value / Formula | Physical / Quantum Basis | Comparative Context in Group 8 / Period 4 |
|---|---|---|---|
| Atomic Number & Symbol | Z = 26 (Fe) | 26 nuclear protons; nuclear charge +26e | Located in Period 4, Group 8 (d-block) |
| Standard Atomic Weight | 55.845 u (g/mol) | Abundance-weighted isotopic nucleon mass | ~30 neutrons in dominant/reference mass number |
| Electron Configuration | [Ar] 3d6 4s2 | Shells: 2 · 8 · 14 · 2 (2 outer-shell e−) | Transition Metals valence orbital architecture |
| Electronegativity & Ionization | χ = 1.83; IE1 = 762 kJ/mol | Pauling bond polarity scale & first valence ionization enthalpy | Governs covalent vs. ionic bond character |
| Melting & Boiling Points | MP: 1811 K; BP: 3134 K | Cohesive lattice energy and intermolecular forces | STP (298 K) phase: SOLID (Liquid range: 1323 K) |
| Principal Oxidation States | +2, +3 | Valence electron donation, sharing, or acceptance | Discovered / First Isolated: Ancient |
Chemical Reactivity, Bonding, and Oxidation States: How Does Iron Form Compounds?
Characteristic Oxidation States and Coordination Chemistry
As a d-block transition metal, partially filled (n−1)d orbitals lie close in energy to the outermost ns subshell, enabling variable oxidation states, d–d electronic transitions, coordination complex formation, and heterogeneous or metalloenzymatic redox catalysis. In chemical compounds, iron exhibits characteristic oxidation states of +2, +3. Depending on the electronegativity difference (Δχ) of its bonding partners—such as Oxygen (χ = 3.44), Fluorine (χ = 3.98), Chlorine (χ = 3.16), Nitrogen (χ = 3.04), Carbon (χ = 2.55), or Hydrogen (χ = 2.20)—iron forms redox-specific oxides, halides, hydrides, or coordination complexes governed by Gibbs free energy (ΔG = ΔH − TΔS).
Nucleosynthesis, Discovery History, and Elemental Origins
First identified or isolated in Ancient, Iron carries a distinct cosmological and geochemical signature. As an element with atomic number Z ≤ 26, iron is forged exothermically inside stars or via cosmic nucleosynthesis before being dispersed into protoplanetary nebulae.
Biological Role and Scientific Applications: Why Is Iron Important in Nature and Technology?
Biochemical Classification: Essential Trace Cofactor
In comparative biochemistry and systems physiology, Iron is classified as Essential Trace Cofactor. Catalytic transition metal or trace nonmetal required in metalloenzyme active sites (redox catalysis, O2 transport, hormone synthesis). Across terrestrial and marine ecosystems, its chemical speciation interacts with electron transport chain, enzymes, electron transport chain, oxidative phosphorylation, reactive oxygen species.
Key Mechanistic Functions and Technological Uses
Endpoint of exothermic stellar fusion in massive stars and dominant constituent of Earth's liquid outer and solid inner core (generating the geomagnetic dynamo). Coordinates O₂ in hemoglobin and transfers electrons in cytochromes. Researchers and students can further investigate Iron's functional role alongside all 118 elements by launching the Interactive Periodic Table & Element Detective Lab on CRV Science Learn.
Frequently Asked Scientific Questions
What is the electron configuration and valence shell structure of Iron (Fe)?
Iron (atomic number Z = 26) has the ground-state electron configuration [Ar] 3d6 4s2, distributing its 26 electrons across 4 shells as 2 · 8 · 14 · 2. Its outermost shell contains 2 electrons, placing Iron in Group 8, Period 4 (d-block) as a member of the Transition Metals. You can watch these 26 electrons orbit the nucleus in real time in the Dynamic Periodic Table Bohr Lab.
What phase of matter is Iron at room temperature, and when does it melt or boil?
At standard room temperature (298 K / 25 °C) and 1 atm pressure, Iron is a crystalline solid. It melts at 1,811 K (+1537.85 °C / +2800.1 °F) and boils at 3,134 K (+2860.85 °C / +5181.5 °F). Using the 0–6,000 K temperature slider in the Interactive Periodic Table, you can observe Iron's exact solid, liquid, and gas transitions relative to all other elements.
How does Iron function in biochemistry, materials science, and technology?
Endpoint of exothermic stellar fusion in massive stars and dominant constituent of Earth's liquid outer and solid inner core (generating the geomagnetic dynamo). Coordinates O₂ in hemoglobin and transfers electrons in cytochromes. In biological systems, it is categorized under Essential Trace Cofactor, with principal oxidation states of +2, +3 and a first ionization energy of 762 kJ/mol.