Dmitri Mendeleev
(web.buddyproject.org/web017/web017/history.html)
History
Dmitri Mendeleev was born in Tobolisk, Siberia in 1834. He was the last of 14 children. After his father went blind, Mendeleev's mother went to work in a glass factory to help him and his brother make money to support the family. When Mendeleev finished high school, his father died and the glass factory his mother worked at burned down. The Mendeleev family were forced to move to St. Petersburg where Dmitri worked tirelessly to get himself into college. In 1863 Mendeleev became a Professor of Chemistry at the Technological Institute in St. Petersburg. He was interested in writing chemistry textbooks (which he did in 1869 about all the known elements) and Mendeleev wanted to show students there were certain patterns in elements.
Discovery
Mendeleev had a large interest in the elements and wanted to find out how they related to each other. Up until this point, there was only one property known that distinguished the elements; that each element has a characteristic atomic weight and this was found by John Dalton in 1805.
Mendeleev started organizing the 63 elements into a table by using the known property of elements-the atomic weight. He put them in rows in order of atomic weight. He also noticed that the elements Florine and Chlorine were next to each other in their two different rows forming a vertical column. This was interesting to him because he already knew that these two elements were similar in their properties. Therefore he noted chemical properties of the elements were grouped into families. He did not know where to put hydrogen so he put it in its own box. He left blank spaces where he thought elements were missing and was therefore able to predict properties of the undiscovered elements that would fit these spaces. These predictions were confirmed when three predicted elements; galium, germanium and scandium were discovered by scientists that looked for them from Mendeleev's clues. He soon became the first creator of the periodic table of elements and became known as a Russian chemist. Later on in his life he got very sick and died shortly after, ending his career.
Periods, Groups, and the Periodic Law
The periodic table was organized into rows and columns, which are called Periods and Groups, respectively. This later became what is known as Periodic Law, which states that properties of elements tend to occur in a pattern as the number of electrons increase in the valence orbital shell. Groups of elements usually display a clear trend in properties, and have the same number of electrons in their outer electron shell. Groups of elements usually have very different masses, while maintaining roughly the same properties. Some exceptions to this "property rule" would be in the groups 13-15 where some of the elements are non-metals, some are metaloids, and some are metals, however these elements still have many similiarties in their properties. This law is important because its helps chemists understand the periodic table better. Without the understanding of this law, chemists would just look at the periodic table as a confusing array of elements.
Periods are of slightly importance and have to do with the number of electron shells. Elements in the same period on the periodic table have similiar masses, but very different properties.
Properties of Elements
Three basic properties of elements Atomic Radius, Ionization Energy, and Electronegativity are clearly organized by the periodic table.
The atomic radius of an element is half the distance between the centers of two atoms that are just touching each other, it is also the distance between the nucleus and the outermost stable electron. The ionization potential is the ammount of electricity needed to make an element give up it's electrons. Electronegativity, although a very scary looking word, is simply a measurement of the amount of "attraction" the element has for bonding with other atoms.
These are represented on the period table, in short by:
When moving left to right along the periodic table,
- The atomic radius decreases
- Ionization potential increases
- Electronegativity increases
When moving down (top to bottom) on the periodic table,
- The atomic radius increases
- Ionization potential decreases
- Electronegativity decreases
Mendeleev's Periodic Table:
(web.fccj.org/~ethall/2045/ch5/mendelev.htm)
The Periodic Table Today:
(http://www.corrosionsource.com/handbook/periodic/periodic_table.gif)
Mendeleevs table vs the Modern Table
When Mendeleev orginally organized the Periodic table, he based the table on the property of atomic weight, which occasionally created errors in his table, but overall provided a stable basis to build the table off of. Later in time, after the discovery of the atomic structure (protons, neutrons, electrons), the table was revised by the atmoic number (based of the # of protons) and found that Mendeleev's table and his are very similar. Today, the periodic table is based off of the atomic number, but without the research and work of Dmitri Mendeleev, the periodic table would not exist.
~Bibliography~
Bliss, Peggy et al. Chemistry. Prentice-Hall: New Jersey. 2002
"Elements and Atoms." Classic Chemistry. July 1996. Le Moyne College. 10/02/06. <http://web.lemoyne.edu/~giunta/EA/MENDELEEVann.HTML>
Ethridge, Frank. "Periodic Table". Encyclopedia of Earth and Physical Sciences. Marshall Cavendish: New York. 1998
"Explore Matter and Molecules." Chemical Heritage Foundation. 2005.
Heilman, Chris. "The Pictorial Periodic Table". <http://chemlab.pc.maricopa.edu/periodic/foldedtable.html>
Knapp, Brian. "The Periodic Law." The Periodic Table. Atlantic Europe Publishing Co.: Danbury, Connecticut. 1998.
Myers, Thomas. Holt Chemistry. Holt: Texas. 2006.
Parkin, Marilyn. "Dimitri Mendeleev." Zephyrus. 9/21/06. 10/03/06. <http://www.zephyrus.co.uk/dimitrimendeleev.html>
"The Periodic Table". ChemCom- Chemistry in the Community. Kendall/Hunt Publishing Co.: Dubuque Iowa. 1998.
"Periodic Properties". About, Inc. The New York Times Company. 2006. <http://chemistry.about.com/library/weekly/aa071802a.htm>
Wilbraham, Antony. "Mendeleev's Periodic Table" Prentice Hall Chemistry. Prentice Hall: Needham, Mass. 2005.
Mendeleev and the periodic table
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