FREE ESSAY ON ARSENIC

ARSENIC

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 trioxide), 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 ingests a
large quantity of arsenic at one time. This condition is characterized by vomiting,
diarrhea and cramps, and may lead to shock, coma and even death. Chronic poisoning occurs
over a longer period of time. In cases of chronic poisoning, aneamia and paralysis may
appear. Other symptoms include skin lesions that are noncancerous and tingling, and
numbness of the soles and palms that develops into a painful condition called neuritis.
With neuritis, reflexes in the extremities may be impaired and even lost. Upon
identification and treatment of the condition, the patient generally recovers within
months, although recovery is not always complete. Prolonged low-dose exposure to arsenic
can also cause cancer, usually skin and lung cancer. Breathing arsenic can irritate the
nose and throat; eye contact can cause red watery eyes and irritation. Long-term exposure
can cause an ulcer or hole in the 'bone' dividing the inner nose, hoarseness, and sore
eyes. BAL (British Anti-Lewisite) was developed as an antidote against arsenic-containing
war gas Lewisite, but it also proved useful in treating common arsenic poisoning. In
medicine, 4-aminobenzene arsenic and 4-hydroxybenzene arsenic compounds are used in
certain infections. An arsenical is one of a group of drugs that contain arsenic and have
been used as a medicine. The best known is Salvarsan, an antisyphilis drug. Carbarsone is
an arsenical used in treating amebic dysentery. Arsenical now are being replaced with
other drugs. 
Supply
Worlds production of arsenic trioxide in 1998 were estimated at 42,000 tonnes, with China
contributing 33%, Belgium 14%, followed by Ghana, 12%, France 7% and Mexico with 7%, at
an estimated price of $0.40/lb. World resources of copper and lead were estimated to
contain about 11 million tonnes of arsenic. Substantial arsenic resources occur in copper
ores in Peru and Philippinesand in copper-gold ores in Chile. Canada also has substantial
arsenic resources, according to the U.S. Geological Survey. The United States imports all
of its arsenic and compounds with more than 95% coming into the country as arsenic
trioxide.
Ground Water Problem
In many places, arsenic is causing a serious problem, that is very hard to control, that
is contaminating ground water. Throughout the world, arsenic in ground water often comes
from natural sources such as bedrock. In some areas, levels of arsenic are increasing in
ground water because of seepage from hazardous waste sites, and arsenic pesticide runoff
also produces elevated arsenic levels in ground water. So, populations relying on ground
water or surface water near geological or man-made sources of arsenic may receive higher
than typical exposure. These areas include industrialized areas and areas where large
quantities of arsenic are disposed of in the landfills, areas of high historical
pesticide use, with soil low in available ferrous and aluminum hydroxides, and areas of
high natural levels of arsenic containing mineral deposits. Population in the area of
copper and other types of metal smelters may be exposed to above-average levels of
arsenic both through the air and as a result of the atmospheric deposition in the soil
and water. Individuals with protein-poor diets or chlorine (of the Vitamin B complex)
deficiency may be more sensitive to arsenic than the general population. 
Milestones
Due to this, and to its being carcinogenic, but also because of the toxicity of arsenic
and its compounds in general, environmental regulation is expected to become increasingly
stringent. While this might adversely affect arsenic demand in the long term, it should
only have a minor near-time effect. 
Bibliography
Chemistry Today: The World Book Encyclopedia Of Science.
Chicago: World Book Inc., 1992.
Lexicon Universal Encyclopedia. New York: Lexicon 
Publications Inc., 1985.
The World Book Encyclopedia