Chem+A+D+Per+Group+5

**THE DISCOVERY OF OXYGEN **

Oxygen was discovered in 1774 by two seperate scientists, Joseph Priestley in England and Carl Wihelm Schelle in Sweden. Schelle, a pharmaceutical chemist, in 1772 conducted numerous experiments involving the heating of substances such mercuric oxide and black magnesia in which oxygen was the byproduct. He like many other scientists of the day believed that air was composed of two different components, one that was combustible and another that wasn't. The one that was combustible he called "fire air" because of it's combustible properties. Meanwhile in England Priestley managed to isolate the element as well and showed off the process to the scientific community, which included Antoine Lavoisier. Oxygen was known as the "new air" and wasn't identified as a separate element. Priestley called it "dephlogisticated air" and tested it on mice and on himself claiming that it was "five or six times better than common air for the purpose of respiration, inflammation, and, I believe, every other use of common atmospherical air". Priestley also made main intresting and important observations about oxygen, he noted that if a lit candle was placed into a sealed container it would burn out quicker. And if a plant was put in the container with the plant, the flame would last longer due to the production of oxygen by the plant.

Antoine-Laurent de Lavoiser aka the father of modern chemistry, was the first person to identify that oxygen is in fact an elem+ent and not "air" as previously believed. He did this through various experiments involving oxidization. In one of these experiments he placed oxygen in a tin container and heated it. There wasn't any increase in overall weight. when he opened the container he saw that air would rush in and the weight of that air would be equivalent of that of the increase in the weight of the tin. The unexpected phenomena showed that oxygen was not a compound but in fact an element still capable of forming bonds. lavoiser went on to call this new element "oxygen" because he believed it was the constituent of all acids thus the prefix "oxys" which in latin means sharp. This was later proven wrong but the name stuck around and remained to be called oxygen.



PHILOGISTON THEORY

Oxygen has been produced by many scientists through out the 17th century but many of them failed to reconigize it as element. The reason why is the Philogiston theory, which is the very first comprehensive theory of chemistry which attempted to be a answer many phenomenas which occur in chemistry. Phlogiston was a substance that chemists believed was responsible for combustion and was found in all combustible substances such as oxygen. philogiston was a near weightless object and was believed to be plentiful in things such as metal and fire. When metal is heated in the presence of air it becomes calx, now known as an oxide. This would result in a loss of wieght in the combustibles because they lose phlogiston. Note, this is the exact opposite of what happened in lavoiser's tin container expirement. This is because some metals when heated become heavier then before. This was explained by having a law which says that some phlogiston has negative wieght. Lavoisier denouncement of this rather complicated theory, unlike Priestley and Schelle allowed him to make the hypothesis that Oxygen, which he concluded to be an element, can react with metal and result in oxidation. He though mistakenly believed that it was the only element responsible for it.

IMPORTANCE OF OXYGEN DISCOVERY: The discovery of Oxygen itself was not actually a "discovery", obviously oxygen has been utilized by living organisms since they existed, the discovery of oxygen however did have an important role in chemistry. The Discovery of Oxygen lead to scientists learning more about combustion and how oxygen reacts with other elements. With the discovery of oxygen scientist also discovered that organisms need oxygen for survival. Rocket enginesand other more complex machines were created due to the discovery of oxygen and it's combustable properties. The discovery of oxygen itself was not as important as the innovations that came with the discovery.

media type="youtube" key="KxMLZXTFkTs&hl=en&fs=1" height="344" width="425" INTERESTING FACTS:


 * 1) Oxygen is the third most abundant element in the Universe
 * 2) Experiments linking combustion and air were first done by the Greeks
 * 3) The Term Oxygen was first used in 1777.

HYPERLINK

http://cti.itc.virginia.edu/~meg3c/classes/tcc313/200Rprojs/lavoisier2/home.html http://www.bookrags.com/Phlogiston_theory [|http://www.britannica.com/EBchecked/topic/527125/Carl-Wilhelm-Scheele] http://acswebcontent.acs.org/landmarks/landmarks/priestley/rebel.html http://www.wired.com/science/discoveries/news/2007/08/dayintech_0801 http://www.youtube.com/watch?v=KxMLZXTFkTs http://www.creationism.org/books/TaylorInMindsMen/TaylorIMMccJosephPriestleyM.jpg http://es.geocities.com/diecam21/Lavoisier.JPG http://www.euchems.org/binaries/Scheele_tcm23-29568.gif