Periodic table › Arsenic
1. Identity and classification
Brittle, crystalline solid with a metallic luster and semiconducting electrical properties
- Name and symbol
- Arsenic (Arsenic) · As
- Atomic number
- 33
- Relative atomic weight / mass number
- 74.922 ± 0.001
- Group · period · block
- 15 · 4 · p
- Category
- Metalloid
- State near room temperature
- Solid
- Stable isotopes
- At least one stable isotope
- CAS number
- 7440-38-2
Square brackets [A] indicate a representative isotope mass number, not an average atomic weight. Neutron counts differ between isotopes.
2. Atomic structure and electron configuration
- Protons · electrons in a neutral atom
- 33 · 33
- Neutrons in reference isotope
- 42 (75As)
- Full electron configuration
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p³- Abbreviated configuration
[Ar]4s² 3d¹⁰ 4p³- Electrons per shell
- 2, 8, 18, 5
- Listed oxidation states
- +5, +3, -3
- Electronegativity
- 2.18 (Pauling)
- First ionization energy
- 947.004 kJ/mol · 9.815 eV
- Electron affinity
- 78.153 kJ/mol
- Covalent radius
- 119 pm
- van der Waals radius
- 185 pm
Configurations of superheavy elements may include theoretical predictions. Different definitions of atomic radius are not interchangeable.
3. Physical and thermal properties
- Density
- 5.776 g/cm³
- Melting point
- Not established
- Boiling point
- Not established
- Crystal structure
- Rhombohedral
- Specific heat
- 0.329 J/(g·K)
- Thermal conductivity
- 50.2 W/(m·K)
- Enthalpy of fusion
- 24.44 kJ/mol
- Enthalpy of vaporization
- 34.76 kJ/mol
- Magnetic ordering
- Diamagnetic
- Mohs hardness
- 3.5
- Speed of sound
- 2100 m/s
Sublimation: 887 K (solid to gas at 1 atm)
Density and structure depend on temperature, pressure and allotrope. 25°C is a room-temperature reference, not STP. Unestablished values are not zero.
4. Chemical behavior and compounds
The listed electron configuration and oxidation states describe atomic structure; compound properties depend on bonding and composition.
Selected compounds: AsO / As₂O₃ (Oxide) · AsClₙ (Chloride) · AsFₙ (Fluoride)
Reaction reference
Oxidation behavior depends on temperature, surface passivation and the chemical environment.
Direct reaction with water is element- and condition-dependent.
5. Isotopes
| Isotope | Status | Natural abundance | Half-life |
|---|---|---|---|
| 75As | Stable | 100% | Stable |
| 76As | Radioactive | — | 26.24 h |
Half-life units: s seconds, m minutes, h hours, d days, Y years. A dash means no natural-abundance value is given, not zero. Listed records are selected ground states; metastable states are distinct.
6. Discovery and occurrence
- Discovery
- Known since antiquity; no exact discovery year
- Scientists associated with discovery
- Known since antiquity
- Location
- Europe / Middle East
- Origin
- Natural
- Listed crustal abundance
- Not established
Minerals and naming reference
Arsenopyrite (FeAsS), Realgar (As₄S₄), Orpiment (As₂S₃)
Named from scientific/historical roots associated with Arsenic (As), discovered or characterized by Albertus Magnus (traditional attribution).
7. Applications
Gallium arsenide (GaAs) optoelectronics, lead-acid battery grid hardener, arsenic trioxide (As₂O₃) acute promyelocytic leukemia therapy
Detailed applications by field
- everyday
- Gallium arsenide (GaAs) optoelectronics, lead-acid battery grid hardener, arsenic trioxide (As₂O₃) acute promyelocytic leukemia therapy
- industry
- Used in metalloid processing, specialized alloys, and chemical manufacturing (Gallium arsenide (GaAs) optoelectronics, lead-acid battery grid hardener, arsenic trioxide (As₂O₃) acute promyelocytic leukemia therapy).
- electronics
- Applied in electronic components, semiconductors, or functional coatings where Arsenic's electronic structure ([Ar] 3d¹⁰ 4s² 4p³) provides target conductivity.
- medicine
- Diagnostic imaging, biomedical instrumentation, or pharmaceutical synthesis research.
- energy
- Utilized in power generation, battery materials, catalysts, or nuclear technology involving Arsenic.
- aerospace
- High-performance materials, structural alloys, or space instrumentation utilizing Arsenic.
- agriculture
- Soil geochemistry analysis, trace micronutrient research, or analytical environmental monitoring.
- science
- Spectroscopic standard, crystallography, and quantum chemistry studies of Period 4 p-block elements.
8. Biological role and safety
Hazard depends on the isotope, chemical form, dose and exposure route.
Elemental substances, ions, compounds and radioisotopes can have different health effects. This is an educational reference; laboratory work requires the material safety data sheet and trained supervision.
Biological role reference
Classified as toxic in human and biological systems.