In-depth, current and accurate information on 112 known chemical elements. For younger and middle school students, yet appropriate for high school students, too.
Publication Date: 2006
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Argon (revised)
By K. Lee Lerner
(2006)
Note: This article, originally published in 1998, was updated in 2006 for the eBook edition.
Overview
Argon is a noble gas. The noble gases are the six elements in Group 18 (VIIIA) of the periodic table. The periodic table is a chart that.... View more
Note: This article, originally published in 1998, was updated in 2006 for the eBook edition.
Overview
Argon is a noble gas. The noble gases are the six elements in Group 18 (VIIIA) of the periodic table. The periodic table is a chart that shows how the chemical elements are related to each other. The noble gases are sometimes called inert gases because Group 18 (VIIIA) elements react with very few other elements. In fact, no compound of argon has ever been produced.
Argon was discovered in 1894 by English chemist John William Strutt, most commonly known as Lord Rayleigh (1842-1919), and Scottish chemist William Ramsay (1852-1916). It was the first of the noble gases to be isolated.
Rayleigh and Ramsay discovered argon by the fractional distillation of liquid air. Fractional distillation is the process of letting liquid air slowly warm up. As the air warms, different elements change from a liquid back to a gas. The portion of air that changes back to a gas at -185.86°C (-302.55°F) is argon.
SYMBOL Ar
ATOMIC NUMBER 18
ATOMIC MASS 39.948
FAMILY Group 18 (VIIIA) Noble gas
PRONUNCIATION AR-gon
Discovery and namingArgon was discovered in 1894. However, English scientist Henry Cavendish (1731-1810) had predicted the existence of argon 200 years earlier. When Cavendish removed oxygen and nitrogen from air, he found that a very small amount of gas remained. He guessed that another element was in the air, but he was unable to identify what it was.
When Ramsay repeated Cavendish's experiments in the 1890s, he, too, found a tiny amount of unidentified gas in the air. But Ramsay had an advantage over Cavendish: he could use spectroscopy, which did not exist in Cavendish's time. Spectroscopy is the process of analyzing light produced when an element is heated. The spectrum (plural: spectra) of an element consists of a series of colored lines and is different for every element.
Ramsay studied the spectrum of the unidentified gas. He found a series of lines that did not belong to any other element. He was convinced that he had found a new element. Meanwhile, Rayleigh was doing similar work at almost the same time. He made his discovery at about the same time Ramsay did. The two scientists decided to make their announcement together. The name argon comes from the Greek word argos, "the lazy one." The name is based on argon's inability to react with anything.
The discovery of argon created a problem for chemists. It was the first noble gas to be discovered. Where should it go in the periodic table? At the time, the table ended with Group 17 (VIIA) at the right. Ramsay suggested that the periodic table might have to be extended. He proposed adding a whole new group to the table. That group would be placed to the right of Group 17 (VIIA).
Ramsay's suggestion was accepted, but it created an interesting new problem for chemists. If there was a new group in the periodic table, where were the other elements that belonged in the group?
Fortunately, chemists had a good idea what these missing elements might look like. All of the elements in a single group are very much like each other. Chemists looked for more inactive gases. Within the next five years, they had found the remaining members of the group: helium, krypton, neon, radon, and xenon.
The symbol A was used for argon until the 1950s when chemists agreed to use the two letter symbol Ar for the element.
Physical propertiesArgon is a colorless, odorless, tasteless gas. Its density is 1.784 grams per liter. The density of air, for comparison, is about 1.29 grams per liter. Argon changes from a gas to a liquid at -185.86°C (-302.55°F). Then it changes from a liquid to a solid at -189.3°C (-308.7°F).
Chemical propertiesArgon is chemically inactive. On rare occasions, and under extreme conditions, it forms weak, compound-like structures.
Occurrence in natureThe abundance of argon in the atmosphere is about 0.93 percent. It is also found in the Earth's crust to the extent of about 4 parts per million.
ExtractionArgon can be produced from liquid air by fractional distillation. It can also be produced by heating nitrogen gas from the atmosphere with hot magnesium or calcium. The magnesium or calcium combines with nitrogen to form a nitride: A little argon always occurs as an impurity with nitrogen. It remains behind because it does not react with magnesium or calcium.
Argon also occurs in wells with natural gas. When the natural gas is purified, some argon can be recovered as a by-product.
IsotopesThree isotopes of argon exist naturally. They are argon-36, argon-38, and argon-40. Isotopes are two or more forms of an element. Isotopes differ from each other according to their mass number. The number written to the right of the element's name is the mass number. The mass number represents the number of protons plus neutrons in the nucleus of an atom of the element. The number of protons determines the element, but the number of neutrons in the atom of any one element can vary. Each variation is an isotope.
Six radioactive isotopes of argon are known also. A radioactive isotope is one that breaks apart and gives off some form of radiation. Radioactive isotopes are produced when very small particles are fired at atoms. These particles stick in the atoms and make them radioactive.
No radioactive isotopes of argon have any practical application. One non-radioactive isotope is used, however, to find the age of very old rocks. This method of dating rocks is described in the potassium entry.
UsesArgon is used in situations where materials need to be protected from oxygen or other gases. A good example is an incandescent lightbulb, which consists of a metal wire inside a clear glass bulb. An electric current passes through the wire, causing it to get very hot and give off light.
Oxygen will combine with the hot metal very easily, forming a compound of the metal and oxygen. This compound will not conduct an electric current very well, thereby causing the lightbulb to stop giving off light.
Argon, however, is used to prevent this from happening. Because argon is inert, it will not react with the hot wire, leaving the metal hot for very long periods of time. The lightbulb will stop giving off light only when the metal breaks. Then it can no longer carry an electric current.
Argon is also used in welding. Welding is the process by which two metals are joined to each other. In most cases, the two metals are heated to very high temperatures. As they get hot, they melt together.
However, as the metals get hot, they begin to react with oxygen. In this reaction, a compound of metal and oxygen is formed. It becomes very difficult to join the two metals if they have formed compounds, but introducing argon into the welding environment improves the bond.
Argon is also used in argon lasers and argon-dye lasers. A laser is a device that produces very bright light of a single color (frequency). An argon laser is used to treat skin conditions. The laser shines a blue-green light on the affected area of the skin. The energy from the laser is absorbed by hemoglobin and converted to heat. (Hemoglobin is the protein pigment in red blood cells. It transports oxygen to the tissues and carbon dioxide from them.) The blood vessels are damaged, but then sealed, prompting them to decompose and be reabsorbed into the body. Unwanted growths are flattened and dark spots are Lightened, with only a small risk of scarring.
An argon-dye laser is used in eye surgery. The color of light produced by the laser can be adjusted with high precision. It can be made to produce light ranging across the green-to-blue color range. Each shade of green or blue has a slightly different frequency. It can penetrate more or less deeply in the eye. The laser can be adjusted to treat a very specific part of the eye. The argon dye is used to treat tumors, damaged blood vessels, conditions involving the retina, and other kinds of eye problems.
CompoundsNo compound of argon has ever been produced.
Health effectsArgon is not known to have any positive or negative effects on the health of plants or animals.
... View lessAntimony (revised)
By K. Lee Lerner
(2006)
Note: This article, originally published in 1998, was updated in 2006 for the eBook edition.
Overview
Antimony compounds have been used by humans for centuries. Women of ancient Egypt used stibic stone, antimony sulfide,.... View more
Note: This article, originally published in 1998, was updated in 2006 for the eBook edition.
Overview
Antimony compounds have been used by humans for centuries. Women of ancient Egypt used stibic stone, antimony sulfide, (Sb2S3), to darken their eyes. Antimony was also used in making colored glazes for beads and glassware. The chemical symbol for antimony was taken from the ancient name for the element, stibium. Not recognized as a chemical element until the Middle Ages, antimony became a common material used by alchemists.
Alchemy was a kind of pre-science that existed from about 500 B.C. to about the end of the 16th century. Alchemists wanted to find a way of changing lead, iron, and other metals into gold. They also wanted to find a way of having eternal life. Alchemy contained too much magic and mysticism to be a real science, but alchemists developed a number of techniques and produced many new materials that were later found to be useful in modern chemistry. Antimony was one of these materials.
SYMBOL Sb
ATOMIC NUMBER 51
ATOMIC MASS 121.75
FAMILY Group 15 (VA) Nitrogen
PRONUNCIATION AN-ti-moh-nee
Discovery and namingCompounds of antimony were known to ancient cultures. They have been found, for example, in the colored glazes used on beads, vases, and other glassware. But these compounds were not widely used until the Middle Ages when they became popular among alchemists. They thought that antimony could be used to convert lead into gold. It was during this period that records about the properties of antimony begin to appear.
The element was probably first named by Roman scholar Pliny (A.D. 23-79), who called it stibium. Muslim alchemist Abu Musa Jabir Ibn Hayyan (c. 721-c. 815) probably first called it antimony—anti ("not") and monos ("alone"). The name comes from the fact that antimony does not occur alone in nature.
Alchemists used secret codes to write about much of their work, so modern scholars do not know a great deal about how antimony was used. The first detailed reports about antimony were published in 1707 when French chemist Nicolas Lemery (1645-1715) published his famous book, Treatise on Antimony.
Physical propertiesAntimony is a silvery-white, shiny element that looks like a metal. It has a scaly surface and is hard and brittle like a non-metal. It can also be prepared as a black powder with a shiny brilliance to it.
The melting point of antimony is 630°C (1,170°F) and its boiling point is 1,635°C (2,980°F). It is a relatively soft material that can be scratched by glass. Its density is 6.68 grams per cubic centimeter.
A metalloid is an element that has characteristics of both metals and non-metals.
Chemical propertiesAntimony is a moderately active element. It does not combine with oxygen in the air at room temperature. It also does not react with cold water or with most cold acids. It does dissolve in some hot acids, however, and in aqua regia. Aqua regia is a mixture of hydrochloric and nitric acids. It often reacts with materials that do not react with either acid separately.
Occurrence in natureAntimony is rarely found in its native (as an element) state. Instead, it usually occurs as a compound. The most common minerals of antimony are stibnite, tetrahedrite, bournonite, boulangerite, and jamesonite. In most of these minerals, antimony is combined with sulfur to produce some form of antimony sulfide (Sb2S3).
The largest producers of antimony are China, Russia, Bolivia, South Africa, and Kyrgyzstan, in that order. The United States produces antimony as a by-product at only one silver mine in Idaho.
The abundance of antimony is estimated to be about 0.2 parts per million, placing it in the bottom fifth among the chemical elements found in the Earth's crust. It is more abundant than silver or mercury, but less abundant than iodine.
IsotopesThere are two naturally occurring isotopes of antimony, antimony-121 and antimony-123. Isotopes are two or more forms of an element. Isotopes differ from each other according to their mass number. The number written to the right of the element's name is the mass number. The mass number represents the number of protons plus neutrons in the nucleus of an atom of the element. The number of protons determines the element, but the number of neutrons in the atom of any one element can vary. Each variation is an isotope.
About 20 radioactive isotopes of antimony are also known. A radioactive isotope is one that breaks apart and gives off some form of radiation. Radioactive isotopes are produced when very small particles are fired at atoms. These particles stick in the atoms and make them radioactive.
Two of antimony's radioactive isotopes are used commercially as tracers. These isotopes are antimony-124 and antimony-125. A tracer is an isotope injected into a living or non-living system. The movement of the isotope can then be followed as it moves through the system. For example, a small amount of antimony-124 could be injected into an oil pipeline. The presence of the isotope can be detected by means of an instrument held above the pipeline. The radiation given off by the isotope causes a light to flash or a sound to occur in the instrument. The movement of the isotope through the pipeline can be followed in this way. If the pipeline has a leak, the tracer will escape from it. Its movement through the soil can be detected.
ExtractionAntimony can be recovered from stibnite with hot iron: About half the antimony produced in the United States is recycled from old lead storage batteries used in cars and trucks.
UsesAntimony is used to make alloys with a number of different metals. An alloy is made by melting and mixing two or more metals. The properties of the mixture are different than those of the individual metals. One of the most common of these alloys is one made with lead. Lead-antimony alloys are used for solder, ammunition, fishing tackle, covering for electrical cables, alloys that melt at low temperatures, and batteries. The manufacture of lead storage batteries, like the ones used in cars and trucks, account for about one-fifth of all the antimony used each year. A small amount of antimony is also used in making transistors, which are found in such consumer electrical devices as computer games, pocket calculators, and portable stereos. A transistor is a solid-state (using special properties of solids, rather than electron tubes) electronic device used to control the flow of an electric current.
Other minor uses of antimony include the manufacture of glass and ceramics and the production of plastics. In glass and ceramics, a small amount of antimony insures that the final product will be clear and colorless. In the production of plastics, antimony is used as a catalyst. A catalyst is a substance used to speed up or slow down a chemical reaction. The catalyst does not undergo any change itself during the reaction.
CompoundsThe most important use of antimony is in making compounds used in the manufacture of flame-retardant materials. Slightly more than half of all antimony goes to this use. These include antimony oxychloride (SbOCl), antimony pentoxide (Sb2O5), antimony trichloride (SbCl3), and antimony trioxide (Sb2O3). These compounds are sprayed on or added to a fabric to make it flame retardant.
Health effectsAntimony and its compounds are dangerous to human health. In low levels, these materials can irritate the eyes and lungs. They may also cause stomach pain, diarrhea, vomiting, and stomach ulcers. At higher doses, antimony and its compounds can cause lung, heart, liver, and kidney damage. At very high doses, they can cause death.
... View lessAmericium (revised)
By K. Lee Lerner
(2006)
Note: This article, originally published in 1998, was updated in 2006 for the eBook edition.
Overview
Americium is called an actinide or transuranium element. It occurs in Row 7 of the periodic table, a chart that shows how the chemical.... View more
Note: This article, originally published in 1998, was updated in 2006 for the eBook edition.
Overview
Americium is called an actinide or transuranium element. It occurs in Row 7 of the periodic table, a chart that shows how the chemical elements are related to each other. The first element in that row is actinium, which explains the name actinide. The term transuranium means "beyond uranium" on the periodic table. Uranium has an atomic number of 92. Any element with an atomic number larger than 92, therefore, is called a transuranium element.
Discovery and namingAmericium was discovered as a by-product of military research during World War I I (1939-45). The U.S. government maintained a major research site at the University of Chicago during the war. Work there led to the development of the first atomic bomb. During that research, a team from the University of California, consisting of Glenn Seaborg (1912- ), Albert Ghiorso (1919- ), Ralph A. James, and Leon O. Morgan (1919- ), discovered a new element, which would eventually be named americium.
SYMBOL Am
ATOMIC NUMBER 95
ATOMIC MASS 243.0614
FAMILY Actinide Transuranium element
PRONUNCIATION am-uh-REE-see-um
Physical propertiesEnough americium has been produced to determine a few of its properties. It is a silvery-white metal with a melting point of about 1,175°C (2,150°F) and a density of about 13.6 grams per cubic centimeter. A number of its compounds have been produced and studied, but only one isotope has considerable practical use outside the laboratory.
Occurrence in natureAll of the transuranium elements, including americium, are synthetically produced. None exist in nature.
IsotopesAll isotopes of americium are radioactive. The most stable is americium-241. Isotopes are two or more forms of an element. Isotopes differ from each other according to their mass number. The number written to the right of the element's name is the mass number. The mass number represents the number of protons plus neutrons in the nucleus of an atom of the element. The number of protons determines the element, but the number of neutrons in the atom of any one element can vary. Each variation is an isotope. A radioactive isotope is one that breaks apart and gives off some form of radiation.
The half life of a radioactive element is the time it takes for half of a sample of the element to break down. The half life of americium-241 is 432.7 years. For example, suppose a laboratory made 10 grams of americium-241. At the end of 432.7 years (one half life), only half would remain. The other half would have changed into a new element.
ExtractionAmericium does not occur naturally.
UsesAmericium-241 is the only isotope of americium of any practical interest. When it decays, it gives off both alpha rays and gamma rays. Alpha rays do not travel very far in air, but gamma rays are very penetrating, much like X rays. The gamma rays from americium-241 are used in portable X-ray machines that can, for example, be taken into oil fields to help determine where new wells should be dug.
Americium-241 is also used to measure the thickness of materials. For instance, a small piece of americium-241 can be placed above a conveyor belt carrying newly made glass. A Geiger counter, a device for counting alpha radiation, is placed below the conveyor belt. If the glass is always the same thickness, the same amount of alpha radiation gets through to the detector. If the glass is thicker than normal, less alpha radiation gets through. If the glass is thinner than normal, more radiation gets through. The detector will register if the glass being produced is too thick or too thin.
The most common use of americium-241 is in certain kinds of smoke detectors. (See accompanying sidebar for more information.)
Where's there's smoke, there should be americium there
One of the simplest and cheapest safety devices found in homes and other buildings is a battery-operated smoke detector. And americium is an important part of it. A small piece of americium oxide made with the americium-241 isotope is sealed inside the smoke detector. The americium-241 gives off alpha particles. The alpha particles strike air molecules, causing them to break apart. The pieces formed in this process—ions—are electrically charged.
The electrically charged ions help carry a current from one side of the detector to the other. The current continues to flow as long as nothing other than air is inside the detector. If smoke enters the detector, the smoke particles absorb some of the alpha particles so that the current is interrupted. When this happens, a buzzer or other sound is set off.
Safety experts recommend changing smoke detector batteries on the same days that Daylight Savings Time begins (in the spring) and ends (in the fall). "Spring forward, fall back, and change your smoke detector battery!"
CompoundsThere are no known commercial uses of americium compounds.
Health effectsAmericium is an extremely toxic element. If swallowed, it is deposited in the bones. There, the radiation it gives off kills or damages cells, causing cancer. People are normally in no danger from smoke detectors containing americium-241. (Indeed, countless lives a year are saved in the United States because of smoke detectors.) The amount of this isotope in a smoke detector is very small. One gram of americium oxide made with americium-241 will make 5,000 smoke detectors.
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