75 Arsenic

Arsenic compounds have been known since at least the days of Ancient Greece and Rome (thousands of years ago). They were used by physicians and poisoners. The compound most often used for both purposes was arsenic sulfide (As 2 3 ).

Arsenic was first recognized as an element by alchemists. Alchemy was a kind of pre-science that existed from about 500 B.C. to about the end of the 16th century. People who studied alchemy—alchemists—wanted to find a way of changing lead, iron, and other metals into gold. They were also looking for a way to have eternal life. Alchemy contained too much magic and mysticism to be a real science, but alchemists developed a number of techniques and produced many new materials that were later found to be useful in modern chemistry.


Credit for the actual discovery of arsenic often goes to alchemist Albert the Great (Albertus Magnus, 1193-1280).

When heated, arsenic does not melt, as most solids do. Instead, it changes directly into a vapor (gas). This process is known as sublimation. However, under high pressure, arsenic can be forced to melt at about 814°C (1,500°F). Arsenic has a density of 5.72 grams per cubic centimeter.

Chemical properties
Arsenic is a metalloid. A metalloid is an element that has properties of both metals and non-metals. Metalloids occur in the periodic table on either side of the staircase line that starts between boron and aluminum.


The abundance of arsenic in the Earth’s crust is thought to be about 5 parts per million. That places it among the bottom third of the elements in abundance in the Earth’s crust.

Arsenic has a fascinating history as a healer and killer. Early physicians, such as Hippocrates (c. 460 B.C -370 B.C. ) and Paracelsus (1493-1541), recommended arsenic for the treatment of some diseases. In more recent times, compounds of arsenic have been used to treat a variety of diseases, including syphilis and various tropical diseases.

Arsenic has a special place in the history of modern medicine. In 1910, German biologist Paul Ehrlich (1854-1915) invented the first drug that would cure syphilis, a sexually transmitted disease. This drug, called salvarsan, is a compound of arsenic. Its chemical name is arsphenamine.

Arsine is an inorganic compound with the formula AsH3. This flammable, pyrophoric, and highly toxic pnictogen hydride gas is one of the simplest compounds of arsenic.



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