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It's Elemental

The Element Arsenic

[Click for Isotope Data]


33 As Arsenic 74.921595

Atomic Number: 33

Atomic Weight: 74.921595

Melting Point: 1090 K (817°C or 1503°F)

Boiling Point: 887 K (614°C or 1137°F)

Density: 5.776 grams per cubic centimeter

Phase at Room Temperature: Solid

Element Classification: Semi-metal

Period Number: 4

Group Number: 15

Group Name: Pnictogen

What's in a name? From the Latin word arsenicum, the Greek word arsenikon and the Arabic word Az-zernikh.

Say what? Arsenic is pronounced as AR-s'n-ik.

History and Uses:

Although arsenic compounds were mined by the early Chinese, Greek and Egyptian civilizations, it is believed that arsenic itself was first identified by Albertus Magnus, a German alchemist, in 1250. Arsenic occurs free in nature, but is most often found in the minerals arsenopyrite (FeAsS), realgar (AsS) and orpiment (As2S3). Today, most commercial arsenic is obtained by heating arsenopyrite.

Arsenic and its compounds are poisonous. They have been used to make rat poison and some insecticides. Small amounts of arsenic are added to germanium to make transistors. Gallium arsenide (GaAs) can produce laser light directly from electricity.

If you were paying careful attention to the physical data listed above, you may have noticed that arsenic's boiling point is lower than its melting point. This occurs because these two temperatures are measured at different atmospheric pressures. When heated at standard atmospheric pressure, arsenic changes directly from a solid to a gas, or sublimates, at a temperature of 887 K. In order to form liquid arsenic, the atmospheric pressure must be increased. At 28 times standard atmospheric pressure, arsenic melts at a temperature of 1090 K. If it were also measured at a pressure of 28 atmospheres, arsenic's boiling point would be higher than its melting point, as you would expect.

Estimated Crustal Abundance: 1.8 milligrams per kilogram

Estimated Oceanic Abundance: 3.7-3 milligrams per liter

Number of Stable Isotopes: 1 (View all isotope data)

Ionization Energy: 9.815 eV

Oxidation States: +5, +3, -3

Electron Shell Configuration:


2s2   2p6

3s2   3p6   3d10

4s2   4p3

Citation and linking information

For questions about this page, please contact Steve Gagnon.