3. Late 18 th century: Lavoisier's list of 28 elements Early 19 th century: John Dalton's list of approximately 60 elements Döbereiner's "triads" of elements with related or similar properties; e.g., Ca, Sr and Ba John Newlands "octaves" or groups of eight elements after which properties seemed to repeat

4. German chemist who, independently of Dmitri Mendeleev, developed a periodic classification of the chemical elements. Though originally educated as a physician, he was chiefly interested in chemistry and physics. (Julius) Lothar Meyer (1830 – 1895)

5. DIMITRI MENDELEEV (1834-1907) Began working on his periodic table of the elements in the late 1860s. Arranged the known 63 elements by their atomic weights and organized them into groups possessing similar properties. Where there were gaps, he correctly predicted the properties for the undiscovered elements (gallium, scandium and germanium).

6. Established the concept of atomic numbers. Henry Moseley (1887-1915) Showed that the ordering of the wavelengths of the x-ray emissions of the elements coincided with the ordering of the elements by atomic number(1913). Developed periodic table based on atomic number.

7. PERIODIC LAW PROPERTIES OF ELEMENTS ARE PERIODIC FUNCTIONS OF THEIR ATOMIC NUMBERS

8. in 1951, Seaborg was awarded the Nobel Prize in chemistry for his work. Element 106 has been named seaborgium (Sg) in his honor. GLENN SEABORG (1912-1999) starting with plutonium in 1940, he discovered all the transuranium elements from 94 to 102 reconfigured the periodic table by placing the actinide series below the lanthanide series

9. THE MODERN PERIODIC TABLE OF ELEMENTS

12. Properties of Major Divisions Metals  lusterous, shiny  typically solids at room temperature (except Hg)  good conductors of heat and electricity  malleable and ductile  tend to lose electrons easily (form cations)

13. Properties of Major Divisions Nonmetals  do not have a metallic luster  poor conductors of heat and electricity  may be solid, liquid or gas at room temperature (majority are gases)  not malleable, not ductile  tend to gain electrons (form anions)

14. Properties of Major Divisions Semi-metals (metalloids) have properties that are intermediate between metals and nonmetals.

22. Elmsley, John, The Elements,3 rd Ed., Clarendon Press, Oxford,1998. Chemistry: Connections to Our Changing World, LeMay, et al., Prentice Hall, 1996. http://www.britannica.com/bcom/eb/article/5/0,5716,53705+1+52397,00.ht ml http://www.crosswinds.net/~smarsden/unit04/l6u4.htm http://www.thirteen.org/archive/hawking/cosmostar/html/cstars_mendel.ht ml http://www.sweethaven.com/chemele/pertab01.html