Re: How do you discover a new element and when do you know that you've found one?

Dear Amanda,

The discovery of new elements has passed through two major stages:

1) In the early days, elements were mostly unknown. With the advance of atomistics (i.e. they theory stating that everything is composed of very small, uniform particles) chemists have started to discover and name elements. Chemical transformations were used to prove that the material at hand is indeed an element, not a molecular compound made of many elements, and that it cannot be further "split" into other elements by chemical means. This process advanced rapidly until many of the naturally occurring elements were discovered.

As a classic example, Chlorine was discovered by Carl Wilhelm Scheele in 1774. Many dates of dicovery and properties of the chemical elements may be obtained from common sources, e.g.
http://www.chemicalelements.com/show/dateofdiscovery.html

2) When the physical theory of an atom had sufficiently advanced, it became possible to predict the existence of elements, based on relatively simple rules. For instance, Helium was discovered spectroscopically in the sun by Sir Joseph Lockyer (England) in 1868. Independent spectroscopic discovery in the sun was done by Pierre Janssen (France). Finally, it was isolated on earth by Sir William Ramsay in 1895.

(also try http://www.spusd.k12.ca.us/chemmybear/element.htm)

The second phase of discovery reached its height with the advances of high-energy physics. Many elements were created and discovered using nuclear reactors, synchrotrons and colliders. Many were discovered by G.T. Seaborg, a prominent nuclear chemist, during 1940-1960 ies. He was a co-discoverer of the elements 94(plutonium), 95(americium), 96(curium), 97(berkelium), 98(californium), 99(einsteinium), 100(fermium), 101(mendelevium), 102(nobelium) and 106 (unnilhexium, tentatively named seaborgium in his honour).

(see e.g. Cf, Md at http://www.ucc.ie/ucc/depts/chem/dolchem/html/elem/elem000.html)

When californium is bombarded with nitrogen nuclei, the resulting element is unnilpentium (#105), which was first named Hahnium after Otto Hahn. As you can see, many man-made elements are named after prominent people or places.

Finally, you can check this link for yet aother table:
http://www.t30.physik.tu-muenchen.de/lehrstuehle/T32/matpack/html/Nuclear/ Elements/discovery.html

Hope it helps.

A.G.E.

Moderator's note:

The page on atomism cited above is a little oversimplified. For one thing it makes it sound like Democritus had experimental reasons for thinking that matter was made up of atoms. He didn't. All Greek physics in those days (with the exception of Archimedes) was purely speculative, based not on experiments but on what seemed correct to the particular philosopher.

Furthermore, Democritus (as far as we can tell) believed in four elements (earth, air, fire and water) just like everybody else. But these elements could never be isolated!

It also makes it sound as though Aristotle was a dork. He wasn't. Philosophy, theology, rhetoric, criticism, deductive and inductive logic, ... (not to mention science) all owe a tremendous debt to his work in one way or another. He was a towering genius, the first person to attempt to systematize all of human knowledge -- and he improved on quite a lot of it.

Real advances in the discovery of chemical elements came with the 17th and 18th Century chemists including Boyle, Lavoisier, Priestley and their contemporaries, who discovered and acted on the Law of Constant Composition. They began to realize that there were more than four elements, and that they could be isolated. In 1804 John Dalton proposed that this Law was best explained by considering matter to be made of atoms.