Place In Periodic Table Essays - Arsenic, Chemical Elements

Place In Periodic Table Phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi) form a group of four elements in Group 5A of the periodic table. They exhibit increasing metallic properties going down the group. Nitrogen (N), which heads the group, is a colorless, odorless, and tasteless gas. Phosphorus is a highly reactive nonmetal, arsenic and antimony are poisonous metalloids, and bismuth is a true metal. Because of the arrangement of the outer electrons in their atoms, each of these elements can form up to five chemical bonds with other elements or groups of elements. Arsenic has an atomic number 33, atomic mass is 74.9216, and it sublimes (passes directly into a vapor without melting) at 613? C. History The Earth's crust contains relatively little arsenic, only about 5.5 parts per million. Arsenic and some arsenic compounds have been known for a long time. Aristotle thought that arsenic was a kind of sulfur. The Latin word arsenicum means yellow orpiment (a pigment containing arsenic and sulfur). While knowledge of arsenic dates back to ancient Greece, it wasn't until the Middle Ages that its poisonous characteristics were described. It was identified by Albert Magnus about 1250, and he described the way to manufacture it. Since then the method has scarcely changed: the mineral arsenopyrite is heated and decomposes with the liberation of arsenic gas. The gas can be condensed on a cold surface. Metallic Arsenic was first produced in the 17th century by heating arsenic with potash and soap. General Properties Arsenic is very similar to antimony and bismuth. It exists in bright, metallic forms that are stable in air. It is found free in nature or in combination with other elements, usually sulfur. It is most often used to improve the strength and hardness of alloys, which are combinations of metals. Arsenic is a gray, shiny metalloid, which is a moderately good conductor of heat and electricity, but gray arsenic is brittle and breaks easily. This is the ordinary, stable form of the element. There are two other allotropes (solid forms)--yellow arsenic and black arsenic, whose modifications have no metallic properties. Occasionally found free in nature, arsenic usually occurs in combination with sulfur, oxygen or certain metals like cobalt, copper, nickel, iron, silver, and tin. In combination, such arsenic is referred to as inorganic arsenic. Arsenic combined with carbon and hydrogen is referred to as organic arsenic. The organic forms are usually less toxic than inorganic forms. The principal arsenic-containing mineral is arsenopyrite. The most widely used arsenic compound is white arsenic, also called arsenic trioxide. It is usually produces as a by-product of the smelting (melting)of copper or lead. At about 400? C it burns with a bluish flame, forming the As2O3 (arsenic triox ide), which is used as a rat poison. In water, arsenic combinations range from being quite soluble (sodium arsenite and arsenic acid) to practically insoluble (arsenic trisulfide). Twenty-one arsenic compounds are considered to be of concern because of their toxicity and/or presence in the environment. Commercial Uses Compounds of arsenic have been used since ancient times for many purposes, including medicines and poisons. In Aristotle's time it was used to harden copper. Orpiment and realgar have long been used as depilatories in the leather industry. When orpiment is rubbed on silver, it gives the surface a golden color. Orpiment thus appears to have one of the properties attributed to the philosophers' stone, and it was therefore an important material for alchemists. Nowadays, it is used in the manufacture of fungicides, weed killers, rat poisons, herbicides, pesticides and insecticides. It is also used to manufacture lead gun shot, to harden the lead, and used in certain types of electrical equipment and to increase the strength of certain alloys. Arsenic is also blended with gallium to produce semiconductors. Effect On Humans Arsenic is a deadly poison and its toxic quality has also been known since ancient times. In the human body it accumulates in the hair and the nails, where it can be detected-even in the bodies of people long dead-by the Marsh test. The Marsh test was devised as a forensic test, where gas arsine is heated to form a metallic mirror of arsenic. Arsenic poisoning may be either acute or chronic. Acute poisoning occurs when a person