Monday, September 2, 2019

Oxygen Essay -- essays research papers

Oxygen Oxygen and its compounds play a key role in many of the important processes of life and industry. Oxygen in the biosphere is essential in the processes of respiration and metabolism, the means by which animals derive the energy needed to sustain life. Furthermore, oxygen is the most abundant element at the surface of the Earth. In combined form it is found in ores, earths, rocks, and gemstones, as well as in all living organisms. Oxygen is a gaseous chemical element in Group VA of the periodic table. The chemical symbol for atomic oxygen is O, its atomic number is 8, and its atomic weight is 15.9994. Elemental oxygen is known principally in the gaseous form as the diatomic molecule, which makes up 20.95% of the volume of dry air. Diatomic oxygen is colorless, odorless, and tasteless. Two 18th-century scientists share the credit for first isolating elemental oxygen: Joseph PRIESTLEY (1733-1804), an English clergyman who was employed as a literary companion to Lord Shelburne at the time of his most significant experimental work, and Carl Wilhelm SCHEELE (1742-86), a Swedish pharmacist and chemist. It is generally believed that Scheele was the first to isolate oxygen, but that Priestley, who independently achieved the isolation of oxygen somewhat later, was the first to publicly announce his findings. The interpretation of the findings of Priestley and the resultant clarification of the nature of oxygen as an element was accomplished by the French scientist Antoine-Laurent LAVOISIER (1743-94). Lavoisier's experimental work, which extended and improved upon Priestley's experiments, was principally responsible for the understanding of COMBUSTION and the establishment of the law of conservation of matter. Lavoisier gave oxygen its name, which is derived from two Greek words that mean "acid former." Lavoisier held the mistaken idea that oxides, when dissolved in water, would form only acids. It is true that some oxides when dissolved in water do form acids; for example, sulfur dioxide forms sulfurous acid. Some oxides, however, such as sodium oxide, dissolve in water to form bases, as in the reaction to form sodium hydroxide; therefore oxygen was actually inappropriately named. NATURAL OCCURRENCE Oxygen is formed by a number of nuclear processes that are believed to occur in stellar interiors. The most abundant isotope of oxygen, with mass 16,... ... are observed to exist over a range of compositions all possessing the same underlying structure. A number of these titanium oxides exhibit more than one crystal structure (polymorphism). The most oxidized compound, titanium, is widely used in the RUTILE form as a white pigment in paints. Ternary oxides, consisting of two metallic elements plus oxygen, are of great interest to solid-state scientists. For example, compounds such as the SPINELS and the PEROVSKITES are studied extensively because of their interesting magnetic and electrical properties. Examples of important ternary oxides are the magnetic FERRITES, whose magnetic properties can be tailored, making them useful in computer memory units. The ferrites are prepared by firing compacted mixtures of iron oxide and one or more metal oxides (such as those of nickel, copper, zinc, magnesium, and manganese). Also of importance in inorganic chemistry are the oxides of the nonmetals. Most of the nonmetals are known to form a wide variety of compounds with oxygen. The nitrogen oxides are undesirable by-products of high-temperature combustion in air (as in an internal combustion engine) and can cause serious environmental pollution.

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