Arsenic
Arsenic (As, atomic number 33) is a Period 4 metalloid (p-block, 74.922 u). Pnictogen chemically analogous to phosphorus; arsenate (AsO₄³⁻) uncouples oxidative phosphorylation by substituting for phosphate in glycolysis, while arsenite (As³⁺) cross-l
Arsenic is a chemical element on the periodic table with the atomic symbol As, atomic number 33, and standard atomic weight 74.922 u. Classified as a Metalloid within Group 15 and Period 4 (p-block), arsenic possesses a ground-state electron configuration of [Ar] 3d10 4s2 4p3 distributed across 4 concentric Bohr electron shells (2 · 8 · 18 · 5) with 5 outer-shell electrons. Pnictogen chemically analogous to phosphorus; arsenate (AsO₄³⁻) uncouples oxidative phosphorylation by substituting for phosphate in glycolysis, while arsenite (As³⁺) cross-links vicinal dithiol lipoamide cofactors.
⚛️ Interactive Periodic Table Lab: Explore Arsenic (As, Z = 33) in the CRV Science Dynamic Periodic Table & Bohr Orbital Lab to visualize its animated 2 · 8 · 18 · 5 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 Arsenic?
Electron Shell Architecture and Ground-State Configuration
A neutral atom of arsenic contains 33 protons in its atomic nucleus balanced by 33 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): 18e−, N (n=4): 5e−), terminating in the directional dumbbell-shaped p-orbital (azimuthal quantum number l = 1) with ground-state configuration [Ar] 3d10 4s2 4p3. Removing the most loosely bound valence electron from an isolated gaseous arsenic atom requires a first ionization energy of 947 kJ/mol, while its tendency to attract shared bonding electrons is quantified by a Pauling electronegativity of 2.18.
Periodic Table Position and Neighboring Elements
Within the periodic table, Arsenic occupies Period 4, Group 15 of the p-block (Metalloids). Along Period 4, it is flanked by Germanium (Ge, Z = 32) and Selenium (Se, Z = 34). Vertically within its periodic family, Arsenic shares valence orbital symmetry and homologous chemical trends with Antimony (Sb). Learners can interactively compare Arsenic's orbital radii, ionization energy, and Pauling electronegativity against all neighboring elements in the Dynamic Periodic Table Lab.
Physical and Thermodynamic Properties: How Does Arsenic 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 arsenic exists as a crystalline solid. As thermal energy increases, its crystal or molecular lattice undergoes solid-to-liquid fusion at a melting point of 1,090 K (+816.85 °C / +1502.3 °F) and transitions to the vapor phase at a normal boiling point of 887 K (+613.85 °C / +1136.9 °F), spanning a liquid thermodynamic range of N/A (sublimes or synthetic regime). 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 Arsenic'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 15 / Period 4 |
|---|---|---|---|
| Atomic Number & Symbol | Z = 33 (As) | 33 nuclear protons; nuclear charge +33e | Located in Period 4, Group 15 (p-block) |
| Standard Atomic Weight | 74.922 u (g/mol) | Abundance-weighted isotopic nucleon mass | ~42 neutrons in dominant/reference mass number |
| Electron Configuration | [Ar] 3d10 4s2 4p3 | Shells: 2 · 8 · 18 · 5 (5 outer-shell e−) | Metalloids valence orbital architecture |
| Electronegativity & Ionization | χ = 2.18; IE1 = 947 kJ/mol | Pauling bond polarity scale & first valence ionization enthalpy | Governs covalent vs. ionic bond character |
| Melting & Boiling Points | MP: 1090 K; BP: 887 K | Cohesive lattice energy and intermolecular forces | STP (298 K) phase: SOLID (Liquid range: N/A (sublimes or synthetic regime)) |
| Principal Oxidation States | +5, +3, -3 | Valence electron donation, sharing, or acceptance | Discovered / First Isolated: Ancient |
Chemical Reactivity, Bonding, and Oxidation States: How Does Arsenic Form Compounds?
Characteristic Oxidation States and Coordination Chemistry
As a p-block metalloid straddling the amphoteric staircase between metals and nonmetals, it exhibits intermediate ionization energy and electronegativity, forming directional covalent networks with semiconducting electronic bandgaps. In chemical compounds, arsenic exhibits characteristic oxidation states of +5, +3, -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)—arsenic 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, Arsenic carries a distinct cosmological and geochemical signature. With atomic number Z = 33 beyond the iron-56 binding-energy peak, arsenic 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).
Biological Role and Scientific Applications: Why Is Arsenic Important in Nature and Technology?
Biochemical Classification: Abiotic / Technological / Synthetic
In comparative biochemistry and systems physiology, Arsenic 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 oxidative phosphorylation, thermodynamics, enthalpy, entropy, chemistry.
Key Mechanistic Functions and Technological Uses
Pnictogen chemically analogous to phosphorus; arsenate (AsO₄³⁻) uncouples oxidative phosphorylation by substituting for phosphate in glycolysis, while arsenite (As³⁺) cross-links vicinal dithiol lipoamide cofactors. Researchers and students can further investigate Arsenic'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 Arsenic (As)?
Arsenic (atomic number Z = 33) has the ground-state electron configuration [Ar] 3d10 4s2 4p3, distributing its 33 electrons across 4 shells as 2 · 8 · 18 · 5. Its outermost shell contains 5 electrons, placing Arsenic in Group 15, Period 4 (p-block) as a member of the Metalloids. You can watch these 33 electrons orbit the nucleus in real time in the Dynamic Periodic Table Bohr Lab.
What phase of matter is Arsenic at room temperature, and when does it melt or boil?
At standard room temperature (298 K / 25 °C) and 1 atm pressure, Arsenic is a crystalline solid. It melts at 1,090 K (+816.85 °C / +1502.3 °F) and boils at 887 K (+613.85 °C / +1136.9 °F). Using the 0–6,000 K temperature slider in the Interactive Periodic Table, you can observe Arsenic's exact solid, liquid, and gas transitions relative to all other elements.
How does Arsenic function in biochemistry, materials science, and technology?
Pnictogen chemically analogous to phosphorus; arsenate (AsO₄³⁻) uncouples oxidative phosphorylation by substituting for phosphate in glycolysis, while arsenite (As³⁺) cross-links vicinal dithiol lipoamide cofactors. In biological systems, it is categorized under Abiotic / Technological / Synthetic, with principal oxidation states of +5, +3, -3 and a first ionization energy of 947 kJ/mol.