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Gaffer Variety:
Elements 4 SN2 006:
By Willie Gaffer:
Last time, I finished with a description of the actinide elements. Now I can carry on with the transition elements. All of the tweener elements in columns 3B through 12B are called transition metals. Transition metal means chemical elements that have valence electrons in two shells instead of only one. The term transition has no particular chemical significance, it is just a handy way to distinguish the similarity of the atomic structures and properties of these elements. The most pronounced similarities are that they are all metals and that most of them are hard, strong, and lustrous. They have high melting and boiling points, and are good conductors of heat and electricity. However, the range in these properties is rather broad.
Many of the elements are technologically important. For example titanium, iron, nickel, and copper, are widely used in structures, manufacturing, and in electrical technology. Another important thing is the transition elements form many useful alloys, with one another and with other metallic elements. Also, most of these elements dissolve in mineral acids. A few, however, such as platinum, silver, and gold, are called “noble” meaning that they are unaffected by nonoxidizing acids. All the elements of the main transition series exhibit variable valence and form stable compounds in two or more formal oxidation states.
There are other metals, which do not fit nicely into the other three groups of metals. These have a group of heir own called, strangely enough, other metals. They are aluminum, gallium, germanium, indium, tin, antimony, thallium, lead, bismuth, and polonium. We will treat them individually later.
We also have a series called other nonmetal. This distinguishes them from the rare earths, actinides, halogens, and noble gases. These elements are boron carbon, nitrogen, oxygen, silicon, phosphorous, sulfur, arsenic, selenium, and tellurium. We will get to these individually.
The halogen elements are the five nonmetallic elements that comprise Group 7A of the periodic table The halogen elements are fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). They were given the name halogen from the Greek roots hal- (“salt”) and gen (“to produce”), because they all produce sodium salts of similar properties, of which sodium chloride, table salt, is the best known. Because of their great reactivity, the free halogen elements are not found in nature. Astatine does not occur in nature at all because it consists only of short-lived radioactive isotopes.
The halogen elements show great resemblances to one another in their general chemical behavior and in the properties of their compounds with other elements. Fluorine is the most reactive of the halogens and, in fact, of all elements, and it has certain other properties that set it apart. Chlorine is the best known of the halogen elements. The free element is widely used as a water purification agent, and it is employed in a number of chemical processes. Sodium chloride, of course, is one of the most familiar of chemical compounds. Fluorides are known chiefly for the controversy over their addition to public water supplies to prevent tooth decay, but organic fluorides are also used as refrigerants and lubricants. Iodine is most familiar as an antiseptic.
The noble gases are the six chemical elements that make up Group 8A of the periodic table. The elements are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). Under ordinary conditions they are colorless, odorless, tasteless, nonflammable gases. They traditionally have been labeled Group 0 in the periodic table because for decades after their discovery it was believed that they had a valence of zero; that is, that their atoms could not combine with those of other elements to form chemical compounds. Their electronic structures and the finding that some of them do indeed form compounds suggest that a more appropriate designation would be Group 8A.
When the members of the group were discovered and identified they were thought to be exceedingly rare, as well as chemically inactive, and therefore were called the rare gases or the inert gases. It is now known, however, that several of these elements are quite abundant on Earth and in the rest of the universe, so the designation rare is misleading. Similarly, use of the term inert has the drawback that it is often applied to gases such as nitrogen and carbon dioxide to connote their non-flammability. In chemistry and alchemy, the word noble long has signified the passivity toward oxygen of a group of metals, such as gold and platinum; it applies in the same sense to the group of gases covered here.
The abundances of the noble gases decrease as their atomic numbers increase. Helium is the most plentiful element in the universe except hydrogen. All the noble gases are present in the Earth's atmosphere and, except for helium and radon, their major commercial source is the air, from which they are obtained by liquefaction and fractional distillation. Most helium is produced commercially from certain natural gas wells. Radon usually is isolated as a product of the radioactive decomposition of dissolved radium compounds (the nuclei of radium atoms spontaneously decay by emitting energy and particles; the particles are the nuclei of helium and radon atoms).
Several important uses of the noble gases rest on their marked lack of chemical reactivity. Their indifference toward oxygen, for example, confers utter non-flammability upon all six noble gases. Although helium is not quite as buoyant as hydrogen, its incombustibility makes it a safer lifting gas for lighter-than-air aircraft. The noble gases, most often helium and argon, the least expensive, are used to provide chemically un-reactive environments for such operations as cutting, welding, and refining of metals and in the handling of other easily attacked materials. Atmospheric oxygen and, in some cases, nitrogen or carbon dioxide would react with the hot metal.
The noble gases absorb and emit electromagnetic radiation in a much less complex way than do other substances. This behavior is utilized in the employment of these gases in discharge lamps and fluorescent lighting devices: if any of them is confined at low pressure in a glass tube and an electrical discharge is passed through it, the gas glows. Neon produces the familiar orange-red color of advertising signs; xenon emits a beautiful blue.
The very low boiling points and melting points of the noble gases make them useful as refrigerants in the study of matter at extremely low temperatures. The low solubility of helium in fluids leads to its use in admixture with oxygen for breathing by deep-sea divers, because helium does not dissolve in the blood. It does not form bubbles upon decompression (as nitrogen does, leading to the condition known as bends). Xenon has been used as an anesthetic, although it is costly, it is nonflammable and readily eliminated from the body. Radon is highly radioactive; its only uses have been those that exploit this property, as, for example, in radiotherapy.
In our next study, we can get into the descriptions of the individual elements.