History+of+the+Periodic+Table

Discovering Elements
Some elements were found in the Ancient Times, such as gold, silver, copper, and mercury. However, some of the elements were only discovered because of the technology that we have today. Becuase many of the elements are found in nature scientists were able to discover them. In a span of 65 years (1800 - 1865) the number of known elements doubled, going from 31 elements to 63 elements.

Classifying Elements
Because there were so many elements scientists began to come up with ways to classify them. In 1969, Russian scientist Dmitri Mendeleev and Germany scientist Lothar Meyer, both created nearly identical classifaction tables. They both found that similar properties both physically and chemically when arranged in increasing atomic weight. This was not the most accurate classifaction because they did not know anything about the atomic number.

Lothar Meyer

Mendeleev
Even though both Meyer and Mendeleev had similar conclusions about the classifaction of the elements, Mendeleev is given more credit because he went further in his discoveries. Mendeleev was so good at classifiying elements that he had to leave blanks in some spots becuase he knew that other elements went there that have not been discovered yet.

Dmitri Mendeleev

Moseley
In 1913, Henry Moseley created the concept of atomic numbers. He found that every element gave off different X ray frequencies, and found that as the frequency increases the atomic mass is greater. Moseley was correct in Identifying the number of protons and electrons in an element. Becuase he figured out how to determine that atomic number, it was easier to organize the periodic table and make it easier to fill in the missing elements.

Henry Moseley

http://www.csvt.qc.ca/patriotes/sciences/scp4/photos_m1/11moseley.gif http://jscms.jrn.columbia.edu/cns/2006-04-18/fido-luxuriantflowinghair/mendeleev/asset_medium http://www.apsidium.com/number/meyer.jpg Chemistry: The Central Science by Brown, LeMay, and Bursten