Arsenic is the third element in the fifteenth column of the periodic table. It is classified as a metalloid because it has some properties similar to metals and some properties similar to nonmetals. The Arsenic atom has 33 electrons and 33 protons with 5 valence electrons in the outermost shell.
Arsenic exists in several isotopes. Isotopes are different structures of the same element. Although they are made of the same element, their different structures can have very different characteristics. For example, carbon has allotropes such as graphite and diamond.
The two most common isotopes of arsenic are yellow and metallic gray. Gray arsenic is a brittle and shiny solid. Arsenic yellow is soft and waxy. Yellow arsenic is reactive and very toxic. It turns to gray arsenic when exposed to light at room temperature. Another allotrope is black arsenic.
| Symbol | As |
| Atomic Number | 33 |
| Atomic Weight | 74.92 |
| Classification | Metalloid |
| Phase at Room Temperature | Solid |
| Density | 5.727 grams per cm cubed |
| Melting Point | 817°C, 1503°F |
| Boiling Point | 614°C, 1137°F |
| Discovered by | Albertus Magnus in 1250 |
Arsenic is perhaps best known for its high toxicity. This means it is very toxic. Many of its compounds are also toxic. Too much arsenic can quickly kill a person, and it has been used in assassinations throughout history. In addition, exposure to small amounts of arsenic over time can cause many health problems. There are many laws governing the treatment and removal of arsenic for industrial use.
Arsenic is found in the earth’s crust. It can be found in a free form, but is very rare. Most arsenic exists in minerals such as realgar, mispickel (arsenopyrite) and orpiment. Arsenic for industrial use is commonly produced as a by-product of gold, silver and copper mining.
Arsenic has been used in the past as an insecticide as well as a wood preservative. Due to environmental concerns, it is no longer used as a pesticide and is being phased out as a wood preservative in the United States. As a wood preservative, copper arsenate helps prevent wood from rotting and prevents termites and other insects from damaging the wood.
Arsenic is combined with gallium to produce gallium arsenide for use in high-speed electronics and optoelectronics. Other uses of arsenic include metal alloying and glass production.
Arsenic has been known since ancient times as part of compounds with sulfur. It is believed to have been first isolated in the Middle Ages by the German philosopher Albertus Magnus in 1250.
Arsenic may get its name from the Greek “arsenikon” meaning “yellow pigment” or “arsenikos” meaning “strong”.
Arsenic occurs naturally in the stable isotope form arsenic-75.
When heated in air, it combines with oxygen to produce arsenic trioxide.
Despite the toxicity of arsenic, very small amounts are considered important for animal health.
Arsenic does not melt under standard pressure, but sublimates directly into a gas. It just melts under high pressure.
We recommend NEVER use, handle or test arsenic or its compounds. It is very dangerous.
