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Iridium is a chemical element on the periodic table with the atomic symbol Ir, atomic number 77, and standard atomic weight 192.22 u. Classified as a Transition Metal within Group 9 and Period 6 (d-block), iridium possesses a ground-state electron configuration of [Xe] 4f¹⁴ 5d⁷ 6s² distributed across 6 concentric Bohr electron shells (2 · 8 · 18 · 32 · 15 · 2) with 2 outer-shell electrons. Most corrosion-resistant metal known and highly siderophile (depleted in Earth's crust but enriched in asteroids). The global iridium anomaly in 66-million-year-old K–Pg boundary clay revealed the Chicxulub asteroid impact that ended non-avian dinosaurs.

⚛️ Interactive Periodic Table Lab: Explore Iridium (Ir, Z = 77) in the CRV Science Dynamic Periodic Table & Bohr Orbital Lab to visualize its animated 2 · 8 · 18 · 32 · 15 · 2 electron shells, simulate live phase transitions from 0 K to 6,000 K, and compare periodic heatmaps across all 118 IUPAC elements.

Electron Shell Architecture and Ground-State Configuration

A neutral atom of iridium contains 77 protons in its atomic nucleus balanced by 77 electrons occupying quantized atomic orbitals. In the Bohr-Sommerfeld and quantum-mechanical orbital models, these electrons populate 6 principal energy shells (K (n=1): 2e⁻, L (n=2): 8e⁻, M (n=3): 18e⁻, N (n=4): 32e⁻, O (n=5): 15e⁻, P (n=6): 2e⁻), terminating in the four-lobed d-orbital manifold (azimuthal quantum number l = 2) with ground-state configuration [Xe] 4f¹⁴ 5d⁷ 6s². Removing the most loosely bound valence electron from an isolated gaseous iridium atom requires a first ionization energy of 880 kJ/mol, while its tendency to attract shared bonding electrons is quantified by a Pauling electronegativity of 2.20.

Periodic Table Position and Neighboring Elements

Within the periodic table, Iridium occupies Period 6, Group 9 of the d-block (Transition Metals). Along Period 6, it is flanked by Osmium (Os, Z = 76) and Platinum (Pt, Z = 78). Vertically within its periodic family, Iridium shares valence orbital symmetry and homologous chemical trends with Cobalt (Co), Rhodium (Rh), Meitnerium (Mt). Learners can interactively compare Iridium's orbital radii, ionization energy, and Pauling electronegativity against all neighboring elements in the Dynamic Periodic Table Lab.

Standard Phase, Melting Point, and Boiling Point Dynamics

At standard ambient temperature and pressure (298.15 K / 25 °C, 1 atm), elemental iridium exists as a crystalline solid. As thermal energy increases, its crystal or molecular lattice undergoes solid-to-liquid fusion at a melting point of 2,719 K (+2445.85 °C / +4434.5 °F) and transitions to the vapor phase at a normal boiling point of 4,403 K (+4129.85 °C / +7465.7 °F), spanning a liquid thermodynamic range of 1684 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 Iridium's state transitions in real time alongside enthalpy and entropy phase equilibria.

Quantitative Atomic and Thermodynamic Parameter Matrix

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, iridium exhibits characteristic oxidation states of +4, +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)—iridium 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 1803, Iridium carries a distinct cosmological and geochemical signature. With atomic number Z = 77 beyond the iron-56 binding-energy peak, iridium is synthesized astrophysically via neutron-capture nucleosynthesis—combining slow neutron capture (the s-process in asymptotic giant branch stars) and rapid neutron capture (the r-process in neutron-star mergers and core-collapse supernovae).

Biochemical Classification: Abiotic / Technological / Synthetic

In comparative biochemistry and systems physiology, Iridium is classified as Abiotic / Technological / Synthetic. No known essential biological role; important in planetary geochemistry, astrophysics, materials science, or nuclear physics. Across terrestrial and marine ecosystems, its chemical speciation interacts with thermodynamics, enthalpy, entropy, chemistry.

Key Mechanistic Functions and Technological Uses

Most corrosion-resistant metal known and highly siderophile (depleted in Earth's crust but enriched in asteroids). The global iridium anomaly in 66-million-year-old K–Pg boundary clay revealed the Chicxulub asteroid impact that ended non-avian dinosaurs. Researchers and students can further investigate Iridium's functional role alongside all 118 elements by launching the Interactive Periodic Table & Element Detective Lab on CRV Science Learn.

What is the electron configuration and valence shell structure of Iridium (Ir)?

Iridium (atomic number Z = 77) has the ground-state electron configuration [Xe] 4f¹⁴ 5d⁷ 6s², distributing its 77 electrons across 6 shells as 2 · 8 · 18 · 32 · 15 · 2. Its outermost shell contains 2 electrons, placing Iridium in Group 9, Period 6 (d-block) as a member of the Transition Metals. You can watch these 77 electrons orbit the nucleus in real time in the Dynamic Periodic Table Bohr Lab.

What phase of matter is Iridium at room temperature, and when does it melt or boil?

At standard room temperature (298 K / 25 °C) and 1 atm pressure, Iridium is a crystalline solid. It melts at 2,719 K (+2445.85 °C / +4434.5 °F) and boils at 4,403 K (+4129.85 °C / +7465.7 °F). Using the 0–6,000 K temperature slider in the Interactive Periodic Table, you can observe Iridium's exact solid, liquid, and gas transitions relative to all other elements.

How does Iridium function in biochemistry, materials science, and technology?

Most corrosion-resistant metal known and highly siderophile (depleted in Earth's crust but enriched in asteroids). The global iridium anomaly in 66-million-year-old K–Pg boundary clay revealed the Chicxulub asteroid impact that ended non-avian dinosaurs. In biological systems, it is categorized under Abiotic / Technological / Synthetic, with principal oxidation states of +4, +3 and a first ionization energy of 880 kJ/mol.