|MadSci Network: Chemistry|
The process of element discovery of the past and of today are quite different. This is because all of the naturally occurring elements have been identified and new ones can only be made and detected in the laboratory.
Historically, the idea of an element came from Robert Boyle in the 1600s. He defined an element as a substance that could not be broken down into simpler substances. Elements were previously defined by Greek alchemists to be air, fire, water, and earth. With Boyle's new idea, the old system was scrapped and new elements were quickly identified. For example, elemental oxygen gas was discovered by Joseph Priestly in the 1700s.
In the early 1800s, John Dalton hypothesized that elements were composed of identical particles. Today, we call these particles atoms. Dalton devised a method to determine atomic weights (which you can find on a periodic table) based on the way elements combined to form simple molecules. This gave a quantifiable way of distinguishing elements. Later, the experiments of Jons Jakob Berzelius corrected and expanded Dalton's table of atomic weights to values that are very close to modern determined values.
Around the turn of the 1900s, great progress was made in modern chemistry. Based on the works of J.J. Thomson and Ernest Rutherford, atomic theory was born. For the first time, scientists began to understand the structure of an atom: the nucleus (protons & neutrons) and the electron cloud. Research in physics and chemistry continues to refine this theory.
By this time, most of the elements known today were identified from natural sources. But in 1937, Carlo Perrier and Emilio Segre artificially produced technetium, which has no natural source. He did this by using a cyclotron (accelerates ions to very high speeds and energies) to bombard molybdenum atoms with deuterium (isotope of hydrogen).
Since then, particle accelerators and cyclotrons have been used to make heavier and heavier elements. Glenn T. Seaborg, an eminent chemist, is famous for discovering or co-discovering most of the transuranium elements (93-103). These elements are radioactive and can be identified based on the particles used to make them and the radioactive decay pattern detected.
Higher atomic numbers continue to be reached. Last year, elements 114, 116, and 118 were discovered. Element 114 was a particularly important milestone, because it is part of an "island of stability" of superheavy elements. This element lasted 30 seconds before decaying; most of the superheavy elements decay in fractions of a second. There is an excellent article about this in the January 2000 edition of Scientific American.
Well, a bit of a long answer, but I hope I was thorough enough. Stay curious and feel free to ask if you have any further questions!
Your MAD Scientist,
Oganessian, YT, Utyonkov, VK, Moody, KJ. "Voyage to Superheavy Island." Scientific American, Jan 2000.
"Three New Elements Discovered in 1999" http://www.infoplease.co m/ipa/A0779259.html
Zumdahl, Steven S. Chemistry, Third Edition. Lexington, MA: D.C. Heath and Company, 1993. pp. 345-347
The Electronic Nobel Museum Project http://www.nobel.se/enm-index.htm l
Try the links in the MadSci Library for more information on Chemistry.