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. Tantalum, symbol Ta, white, ductile, malleable metallic element. Tantalum is one of the transition elements of the periodic table . The atomic number of tantalum is 73. Tantalum was first obtained in pure form in 1820 by the Swedish chemist Baron Jöns Jakob Berzelius , who heated potassium tantalifluoride, with excess potassium. PROPERTIES AND OCCURRENCE Tantalum is soluble in fused alkalies, insoluble in sulfuric, hydrochloric, and nitric acids, and soluble in hydrofluoric acid. It ignites in air to form tantalum pentoxide (sometimes referred to as tantalum(V) oxide or tantalic acid anhydride), a white infusible substance that combines with metallic oxides or hydroxides to form compounds called tantalites. Tantalic acid (also know as tantalum(V) oxide hydrate), is a gelatinous precipitate that has a varying number of water molecules associated with each tantalum pentoxide molecule. Tantalum melts at about 2996° C (about 5425° F), boils at about 5425° C (about 9797° F), and has a sp

. Technetium, symbol Tc, radioactive metallic element, the first element to be created artificially. The atomic number of technetium is 43. Technetium is one of the transition elements of the periodic table . In 1937 Emilio Segrè and Carlo Perrier created technetium by bombarding molybdenum targets with deuterons (particles consisting of a proton and a neutron ). Because technetium is not part of the decay series of any naturally radioactive element (see Radioactivity ), scientists had thought that technetium does not occur in nature. In 1988, however, minute quantities of it were detected in ore from a deep molybdenum mine in Colorado. Isotopes ranging in mass number from 90 to 111 are known; the most common isotope has a mass number of 98. Technetium forms oxides, sulfides, and technetiates, such as ammonium technetiate. Compounds and alloys containing technetium oxide can prevent the corrosion of iron by water. Technetium-99 is used for imaging in medicine. Technetium melts at abo

. Synthetic Fuels, liquid or gaseous fuels extracted or fabricated from solid earth materials that are rich in hydrocarbons —compounds containing hydrogen and carbon. Although similar in composition to gasoline , synthetic fuels are not refined from petroleum , but are extracted instead from coal, oil shale, tar sands, natural gas, and biomass (plants and plant-derived substances). For example, coal can be converted into liquid fuel by a process called liquefaction, and oil can be extracted from oil shale by a process called retorting. Natural gas is converted into fuel-ready liquid by using gas-to-liquids technology. Like petroleum-based fuels, synthetic fuels can be used in a variety of applications in transportation, manufacturing, businesses, and homes. Because producing synthetic fuels is more costly than refining petroleum, however, the use of synthetic fuels is not widespread.

. Tellurium (Latin tellus,”earth”), symbol Te, silver-white, brittle, semimetallic element. The atomic number of tellurium is 52. Tellurium was first discovered in 1782 by the German scientist Franz Joseph Müller von Reichenstein; it was recognized as an element and given its name in 1798 by the German chemist Martin Heinrich Klaproth . PROPERTIES AND OCCURRENCE Tellurium is a comparatively stable element, insoluble in water and hydrochloric acid but soluble in nitric acid and aqua regia . Tellurium reacts with an excess of chlorine to form tellurium dichloride, and tellurium tetrachloride. It is oxidized by nitric acid to produce tellurium dioxide, and by chromic acid to produce telluric acid. In combination with hydrogen or certain metals, it forms tellurides such as hydrogen telluride and sodium telluride. Tellurium melts at about 452° C (about 846° F), boils at about 1390° C (about 2534° F), and has a specific gravity of 6.25. The atomic weight of tellurium is 127.60. Tellurium ra

. Terbium, symbol Tb, metallic element with an atomic number of 65. Terbium is one of the rare earth elements in the lanthanide series of the periodic table . Terbium was discovered in 1843 by the Swedish chemist Carl Gustav Mosander. It ranks about 58th in natural abundance among the elements in crustal rock. It occurs in minute quantities as a white oxide known as terbia, in such minerals as gadolinite. Terbium has potential applications in alloys , refractory (high-temperature) materials, and electronic apparatus. Terbium melts at about 1356° C (about 2473° F), boils at about 3230° C (about 5846° F), and has a specific gravity of 8.23. The atomic weight of terbium is 158.925.

. Thallium (Greek thallos, “young shoot”), symbol Tl, soft, malleable metallic element that acquires a bluish-gray color upon exposure to the atmosphere. Thallium is in group 13 (or IIIa) of the periodic table . The atomic number of Thallium is 81. Thallium was discovered spectroscopically in 1861 by the British chemist Sir William Crookes. It was isolated by Crookes and, independently, by the French chemist Claude August Lamy in 1862. PROPERTIES AND OCCURRENCE Thallium forms a hydroxide in water, and is soluble in nitric acid and sulfuric acid . It forms two series of salts, represented by thallous chloride, TlCl, and thallic chloride, which are univalent and trivalent, respectively. Thallous oxide, a black solid that, when molten, attacks glass and porcelain, is made by heating thallium in air at very high temperatures. Thallium has a high index of refraction and is therefore important in the manufacture of several types of optical glass. Thallium ranks 60th in abundance among the e

. Thorium, symbol Th, radioactive metallic element with an atomic number of 90. Thorium is a member of the actinide series of the periodic table . Thorium was discovered (1828) by the Swedish chemist Baron Jöns Jakob Berzelius . The element is dark in color, slowly attacked by water, soluble in hydrochloric and sulfuric acids, and slightly soluble in nitric acid. It ranks 39th in abundance among the elements in the crust of the earth. Thorium melts at about 1750° C (about 3182° F), boils at about 4850° C (about 8762° F), and has a specific gravity of 11.8. The atomic weight of thorium is 232.04. Small quantities of thorium are found in thorite, or thorium silicate; in orangite, a variety of thorite; and in thorianite, a radioactive mineral composed of thorium oxide and uranium. Thorium has isotopes ranging in mass number from 212 to 236. Thorium-232 occurs naturally, has a half-life of about 14 billion years, and is the first member of the radioactive-decay series, ending with the sta