The Element Arsenic
[Click for Isotope Data]
Atomic Number: 33
Atomic Weight: 74.92160
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
3s2 3p6 3d10