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Astatine is a chemical element on the periodic table with the atomic symbol At, atomic number 85, and standard atomic weight 210 u. Classified as a Halogen within Group 17 and Period 6 (p-block), astatine possesses a ground-state electron configuration of [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁵ distributed across 6 concentric Bohr electron shells (2 · 8 · 18 · 32 · 18 · 7) with 7 outer-shell electrons. Rarest naturally occurring element in Earth's crust (<1 gram exists across the entire crust at any moment as a transient decay intermediate). ²¹¹At (t₁/₂ = 7.21 h) is investigated for targeted alpha-particle cancer radiotherapy.

⚛️ Interactive Periodic Table Lab: Explore Astatine (At, Z = 85) in the CRV Science Dynamic Periodic Table & Bohr Orbital Lab to visualize its animated 2 · 8 · 18 · 32 · 18 · 7 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 astatine contains 85 protons in its atomic nucleus balanced by 85 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): 18e⁻, P (n=6): 7e⁻), terminating in the directional dumbbell-shaped p-orbital (azimuthal quantum number l = 1) with ground-state configuration [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁵. Removing the most loosely bound valence electron from an isolated gaseous astatine atom requires a first ionization energy of 899 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, Astatine occupies Period 6, Group 17 of the p-block (Halogens). Along Period 6, it is flanked by Polonium (Po, Z = 84) and Radon (Rn, Z = 86). Vertically within its periodic family, Astatine shares valence orbital symmetry and homologous chemical trends with Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I). Learners can interactively compare Astatine'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 astatine exists as a crystalline solid. As thermal energy increases, its crystal or molecular lattice undergoes solid-to-liquid fusion at a melting point of 575 K (+301.85 °C / +575.3 °F) and transitions to the vapor phase at a normal boiling point of 610 K (+336.85 °C / +638.3 °F), spanning a liquid thermodynamic range of 35 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 Astatine'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 Group 17 p-block halogen with an ns² np⁵ valence shell (one electron short of a closed octet), it exhibits high electron affinity and oxidizing power, forming halide (−1) anions, covalent organohalogens, and interhalogen compounds. In chemical compounds, astatine exhibits characteristic oxidation states of -1, +1. 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)—astatine 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 1940, Astatine carries a distinct cosmological and geochemical signature. With atomic number Z = 85 beyond the iron-56 binding-energy peak, astatine 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, Astatine 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

Rarest naturally occurring element in Earth's crust (<1 gram exists across the entire crust at any moment as a transient decay intermediate). ²¹¹At (t₁/₂ = 7.21 h) is investigated for targeted alpha-particle cancer radiotherapy. Researchers and students can further investigate Astatine'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 Astatine (At)?

Astatine (atomic number Z = 85) has the ground-state electron configuration [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁵, distributing its 85 electrons across 6 shells as 2 · 8 · 18 · 32 · 18 · 7. Its outermost shell contains 7 electrons, placing Astatine in Group 17, Period 6 (p-block) as a member of the Halogens. You can watch these 85 electrons orbit the nucleus in real time in the Dynamic Periodic Table Bohr Lab.

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

At standard room temperature (298 K / 25 °C) and 1 atm pressure, Astatine is a crystalline solid. It melts at 575 K (+301.85 °C / +575.3 °F) and boils at 610 K (+336.85 °C / +638.3 °F). Using the 0–6,000 K temperature slider in the Interactive Periodic Table, you can observe Astatine's exact solid, liquid, and gas transitions relative to all other elements.

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

Rarest naturally occurring element in Earth's crust (<1 gram exists across the entire crust at any moment as a transient decay intermediate). ²¹¹At (t₁/₂ = 7.21 h) is investigated for targeted alpha-particle cancer radiotherapy. In biological systems, it is categorized under Abiotic / Technological / Synthetic, with principal oxidation states of -1, +1 and a first ionization energy of 899 kJ/mol.