Named from the Greek oxys + genes, "acid-former", oxygen was discovered in 1772 by Scheele and independently by Priestley in 1774.
Oxygen is the most common element in the earth's crust and makes up about 20% of the air we breathe. Historically the discovery of oxygen as an element essential for combustion stands at the heart of the phlogiston controversy.
Oxygen is a gas at room temperature and is colorless, odorless and tasteless. Liquid oxygen has a slight blue color. Virtually every element known forms a compound with oxygen except for some of the noble gases. Two allotropes of oxygen are known. The ordinary oxygen in the air (O2) and the ordinary ozone in air and above it (O3). Ozone occurs naturally in the upper atmosphere where it acts as a shield protecting the earth's biosphere from ultraviolet radiation. Closer to the surface ozone can be a nuisance as it is very reactive. But in a controlled environment it is also handy: it makes a good bleach and disinfectant.
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Known from ancient times (mentioned in the Hebrew scriptures as brimstone) sulfur was classified as an element in 1777 by Lavoisier. Pure sulfur is tasteless and odorless with a light yellow color. Samples of sulfur often encountered in the lab have a noticeable odor. Sulfur is the tenth most abundant element in the known universe.
There are three allotropic forms of sulfur. Two are crystalline and one is amorphous (sometimes called "plastic" sulfur). This last form gradually reverts to one of the more stable crystalline forms. Most sulfur is recovered directly as the element from underground deposits by injecting super-heated water and piping out molten sulfur (sulfur melts at 112o C).
Perhaps the most significant compound of sulfur used in modern industrialized societies is sulfuric acid (H2SO4). Sulfur dioxide (SO2) finds practical applications in bleaching and refrigeration but it is also a nuisance gas resulting from the burning of sulfurous coals. Sulfur dioxide gas then reacts with the water vapor in the air to produce a weak acid, sulfurous acid (H2SO3) which contributes to the acid rain problem.
Other than sulfuric acid, perhaps the most familiar compound of sulfur in the chemistry lab is the foul-smelling hydrogen sulfide gas, H2S, which smells like rotten eggs.
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Selenium was discovered by Berzelius in 1818. It is named for the Greek for "moon", selene. Most selenium is recovered from the electrolytic copper refining process. This is usually in the form of the red allotrope. There are at least two other allotropes of the element, including a semi-metallic state.
Selenium is an important semi-conductor which is particularly sensitive to light. Thus it finds applications that range from light sensors to xerography.
In large amounts the element is toxic, but it is a trace element in living organisms.
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Discovered by von Reichenstein in 1782, tellurium is a brittle metalloid that is relatively rare. It is named from the Latin tellus for "earth".
Tellurium can be alloyed with some metals to increase their machinability and is a basic ingredient in the manufacture of blasting caps.
Elemental tellurium is occasionally found in nature but is more often recovered from various gold ores, all containing AuTe2.
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Polonium was discovered in 1898 by Marie Curie and named for her native country of Poland. The discovery was made by extraction of the remaining radioactive components of pitchblende following the removal of uranium. There is only about 10-6 g per ton of ore! Current production for research purposes involves the synthesis of the element in the lab rather than its recovery from minerals. This is accomplished by producing Bi-210 from the abundant Bi-209. The new isotope of bismuth is then allowed to decay naturally into Po-210. the sample pictured above is actually a thin film of polonium on stainless steel.
Although radioactive, polonium has a few commercial uses. You can buy your own sample of polonium at a photography store. It is part of the special anti-static brushes for dusting off negatives and prints.
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