Atomic Properties of As
- Atomic Number of As
- 33
- Atomic Mass of As
- 74.9220 u
- Electron Configuration
- [Ar] 3d10 4s2 4p3
- Electronegativity
- 2.18
- Block
- p-block
- Group
- 15
- Period
- 4
Arsenic cannot be summarized by a skull-and-crossbones. Elemental arsenic, arsenite, arsenate, arsine gas, and organoarsenic compounds differ in mobility and toxicity. Inorganic arsenic in drinking water is a major health concern because long-term exposure raises risks of cancer and other disease. Arsine is acutely poisonous. Some organic arsenic compounds found in seafood are much less toxic. Identifying the species matters before interpreting a concentration.
Groundwater can acquire arsenic naturally when minerals and changing chemical conditions release it from rock and sediment. Contamination also comes from mining, smelting, and historical pesticides or wood preservatives. Arsenic has no smell or taste in water, so laboratory testing and treatment provide protection, not sensory clues or dramatic folklore.
Useful chemistry remains. Gallium arsenide is a compound semiconductor whose electrons move efficiently and whose direct band gap suits LEDs, lasers, solar cells, and high-frequency electronics. The device contains arsenic in a crystal lattice; this does not erase manufacturing and disposal controls. Arsenic has also hardened lead alloys and once appeared widely in pigments and pesticides, uses curtailed as harms became clearer.
Natural arsenic is entirely stable arsenic-75. The metalloid occurs in minerals such as arsenopyrite and has gray, yellow, and black allotropes. Its history reaches antiquity, long before modern toxicology.
Arsenic is a Contrarian because a familiar label conceals speciation. The same element can be locked in a semiconductor, mobilized into groundwater, or transformed into a highly toxic gas. Good chemistry replaces the question “Is arsenic poisonous?” with “Which arsenic compound, at what dose, by what route?”