Arsenic
Element 33 · Metalloid
Arsenic is a steel-gray metalloid infamous as a poison — arsenic trioxide is tasteless, odorless, and was historically almost undetectable, earning it the grim nickname inheritance powder. Its toxicity comes from mimicking phosphate in cells and binding to sulfur in enzymes.
Yet arsenic is also technologically valuable: combined with gallium it forms gallium arsenide, a semiconductor essential for lasers and high-speed electronics. At room pressure the gray form sublimes rather than melting, passing directly from solid to vapor at 615 °C. All arsenic compounds demand careful handling.
Key facts
| Atomic number | 33 |
|---|---|
| Atomic weight | 74.922 |
| Category | Metalloid |
| Group / Period | 15 / 4 |
| Block | p |
| Electron configuration | [Ar] 3d10 4s2 4p3 |
| Common oxidation states | +5, +3, -3 |
| State at STP | Solid |
| Electronegativity | 2.18 |
| Atomic radius | 114 pm |
| Density | 5.727 g/cm³ |
| Melting point | 817 °C (sublimes at 1 atm) |
| Boiling point | 615 °C (sublimes) |
Occurrence
Arsenic occurs in minerals such as arsenopyrite, realgar, and orpiment, and is recovered as a byproduct of smelting metal ores. It also contaminates groundwater in parts of South Asia, where it is a serious public-health problem. It never occurs as a pure free element in usable deposits.
Applications
Gallium arsenide semiconductors power lasers, LEDs, and phone chips
Pressure-treated wood historically used chromated copper arsenate preservatives
Lead shot and battery grids are hardened with small arsenic additions
Herbicides and insecticides once relied on arsenic compounds
Semiconductor doping uses arsine gas in controlled manufacturing
Common compounds
- arsenic trioxide
- arsenic acid
- sodium arsenite
- gallium arsenide
Arsenic was once called 'inheritance powder' because it was a nearly undetectable poison.
Data source: IUPAC standard atomic weights 2021