The element arsenic is a semi-metallic substance with atomic number 33 and atomic mass 74.92. Its chemical symbol is As. It is also referred to as metalloid because its physical and chemical properties are intermediate to metals and non-metals. In the periodic table, arsenic is found in the same group as nitrogen and phosphorus. The credit for discovering this element goes to Albertus Magnus who isolated this element in the year 1250.
Arsenic is available in a free state in nature in a variety of crystal structures. However, it is found more commonly in the form of arsenide and arsenate compounds. Arsenopyrite is one such mineral of arsenic in which it is present in the arsenide form. It is extracted from arsenopyrite by first roasting it in the presence of air and then without air.
Properties of Arsenic and its Compounds
Arsenic exhibits allotropic properties, which means it exists in a number of different forms. Out of its several allotropic forms, there are three major forms that are most commonly found. They are - yellow, metallic gray and black arsenic. The melting point of arsenic is higher than that of its boiling point. For this reason, if it is heated under normal atmospheric pressure, it gets converted directly into its gaseous state without forming any liquid.
Chemical properties of arsenic are quite similar to that of phosphorus. On heating in air, arsenic oxidizes to give arsenic trioxide and is released in the form of fumes that have a garlic-like smell. The oxides of arsenic (As2O3 and As2O5) are colorless and odorless compounds. They are found in crystalline forms and are hygroscopic in nature, that is, they readily absorb moisture from the air. Its oxides dissolve in water to give acidic solutions. Its hydrides are unstable in nature. Arsenic acid is a weak form of acid.
Uses of Arsenic and its Compounds
The element arsenic is used for the preservation of wood. It is mainly due to the poisonous effect it has on insects, bacteria and fungi. Nevertheless, many countries like the European Union and the United States have banned its use because of the environmental problems that it causes. In agriculture, organic form of arsenic compounds are used as insecticides. Gallium arsenide is used as a semiconductor material in integrated circuits. These circuits are much more faster than circuits made in silicon.
Despite its toxicity, arsenic has some medicinal value too, and has been used for the past so many centuries in treating various diseases. Presently, it is used for the treatment of cancer, particularly leukemia. It is a key ingredient of medicines that are used for curing psoriasis. Arsenic-74 is an isotope of arsenic which is used to locate tumors.
Hazardous Effects of Arsenic
Arsenic and many of its compounds are highly toxic in nature. On entering into the human body, it inhibits the production of essential ATP (Adenosine Triphosphate) molecules. These ATP molecules are responsible for carrying out various vital functions in our body. Interference in the metabolic process of the body can cause death due to multiple organ failure. However, if treated on time, arsenic poisoning can be cured easily.
Various surveys conducted have revealed millions of cases of arsenic poisoning through drinking of arsenic contaminated groundwater. These instances are particularly high in Bangladesh and its neighboring countries.