Arsenic, antimony, and bismuth

Arsenic, antimony, and bismuth exist in bright, metallic forms that are stable in air. They are found free in nature or in combination with other elements, usually sulfur. They are most often used to improve the strength and hard­ness of alloys, which are combinations of met­als.

Arsenic is a gray, shiny metalloid. This is I the ordinary, stable form of the element. There are two other forms—yellow arsenic and black

Major groups of elements: Phosphorus to bismuth 49

arsenic. Occasionally found free in nature, ar­senic usually occurs in combination with sul­fur, oxygen, or certain metals. Arsenic is a deadly poison. It is used in the manufacture of fungicides, weedkillers, rat poisons, and insec­ticides. It is also used in certain types of elec­trical equipment and to increase the strength of certain alloys.

Antimony is a bluish-white, brittle metal. This is its more common pure form. It also ex­ists as black or gray antimony, a black powder. Antimony is most often found, however, in combination with sulfur in a mineral called stibnite. Compounds containing antimony are used in refrigerators, air conditioners, paints, aerosol sprays, and flame-proofing materials. Antimony-lead alloys are used in making metal for printing type, batteries, and electric cables.

Bismuth is a pinkish-white, brittle metal. Al­though it is found free in nature and in certain ores, such as bismite, it is generally obtained as a by-product in refining tin, lead, copper, silver, and gold ores. Bismuth is most often used to make alloys that melt at low tempera­tures. These alloys are used to make safety plugs for steam boilers and automatic sprin­kler systems. They are also used in making electrical fuses. Bismuth finds uses in found­ries and in nuclear reactors. It is also used in some medicines, cosmetics, and certain drugs.

B Strike-anywhere match

C Safety match

V_

Phosphorus

sulfide

tip

Potassium ""chlorate and sulfur

Antimony sulfide >-and potassium dichromate

-Red phosphorus and abrasive powder

Antimony compounds

were known to the ancient Egyptians. They used a sul­fide (stibnite) as black eye makeup, a feature reflected in their sculpture (far left!.

In the Marsh test(left), de­vised as a forensic test in cases of suspected arsenic poisoning, the gas arsine is heated to form a metallic mirror of arsenic.

Phosphorushas long been used in matches. The origi­nal phosphorus match (A)— now illegal—had a white phosphorus tip. It was banned because of the dan­ger of phosphorus poison­ing to match workers. A strike-anywhere match (B) uses phosphorus sulfide in­stead. In safety matches (Q, the nonpoisonous red phos­phorus is in the striking sur­face.

The two main allotropes of phosphorus(below) have different molecular structures. White phospho­rus (A) exists as tetrahedrally joined groups of four atoms. Red phosphorus (B) consists of chains.

Fact entries

Phosphoruswas first iso­lated from urine by the Ger­man alchemist Hennig Brand in 1669. In 1860, it was discovered independ­ently by the English chemist Robert Boyle. The name comes from the Creek phosphoros, meaning light-bearer. The white form

glows in the dark. At. no. 15; at. mass 30.9738; m.p. (white) 44.1° C; b.p. (white) 280° C; m.p. (red) 600° C (under pressure).

Arsenicwas identified by Albert Magnus about 1250. The Latin word arsenicum means yellow orpiment (a

pigment containing arsenic and sulfur). At. no. 33; at. mass 74.9216; sublimes (passes directly into a vapor without melting) at 613° C

Antimonyoccurs mainly as its sulfide mineral stibnite (Latin stibnum), from which it derives its chemical sym-

bol Sb. It was known to the Creeks and Romans. At. no. 51; at. mass 121.75; m.p. 630.74° C; b.p. 1586.85° C

Bismuthwas known in the ancient world. It was iso­lated by Caspar Newmann (1683-1737). Its name may derive from the Old German

vissmuth (white matter). At. no. 83; at. mass 208.98; m.p. 271.3° C; b.p. about 1560+5° C.

Oxygenheads Group 6A of the periodic table. It is more reactive than nitrogen, its neighbor to the left in Croup 5A, but less so than fluorine on the right.

Oxygen

Oxygen (O) is a colorless, odorless, and taste­less gas. It is one of the most abundant ele­ments on the earth. It makes up about 23 per cent by weight and 21 per cent by volume of the atmosphere, 89 per cent by weight of water, and almost half the weight of the earth's crust. In air, oxygen is found in molecules that contain two atoms of oxygen. Elsewhere, it is found combined with many other elements as oxides, in various salts, and as an important part of living matter.

In the periodic table, oxygen lies at the head of Croup 6A. By taking up two electrons from other elements, it can acquire a full outer shell of electrons and a stable structure. By doing this, it can combine with almost every other element—both metals and nonmetals. Compounds of the other elements and oxygen are known as oxides. These can be formed in a variety of ways. For example, finely divided iron or carbon burn in pure oxygen to form oxides. Iron left in the air slowly rusts, also to form iron oxide. Such reactions with oxygen are known as oxidation. Most combustion re­actions, such as ordinary wood fires, involve oxidation. In these cases, a very fast burning process also gives out large amounts of heat and light. The decay of plant and animal tissue also involves oxidation, but without the rapid release of heat and light.

Date: 2015-12-11; view: 1344