3. Dmitri Mendeleev (1869) In 1869 Mendeleev and Lothar Meyer (Germany) published nearly identical classification schemes for elements known to date. The periodic table is base on the similarity of properties and reactivities exhibited by certain elements. Later, Henri Moseley ( England,1887-1915) established that each elements has a unique atomic number, which is how the current periodic table is organized. http://www.chem.msu.su/eng/misc/mendeleev/welcome.html
10. 3. Trend in Ionization Energy Ionization energy: The energy required to remove the valence electron from an atomic specie.
11. 4. Trend in Electron Affinity Electron affinity is a measure of the energy that is released when an atom acquires an electron. We say that the more energy is released, the more readily the atom becomes an anion.
![The Periodic Table and the Elements ,[object Object],[object Object],[object Object]](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)