1. The Periodic Table A Short History

2. End of 1700s: Had identified 30 elements Lavoisier separated metals and nonmetals Some known since prehistoric times Cu O2O2 Ag Au C H2H2 N2N2

3. Early 1800 56 known elements New methods such as atomic spectra used to identify new elements

4. German Chemist J.W. Dobereiner (1780-1849) Observed several triads 3 elements with similar properties where the middle element had average properties

5. Triads Element Atomic Mass Density Cl 35.5amu 1.56 g/L Br 79.9amu 3.12 g/L I 126.9amu 4.95 g/L Ca 40.1amu 1.55 g/L Sr 87.6amu 2.70 g/L Ba 137.0amu 3.50 g/L

6. 1865 J.A.R. Newlands (1837-1898) 62 Known elements When elements were arranged by increasing atomic mass, the properties repeated every 8 th element Called the phenomena the “Law of Octaves” “Law of Octaves”

7. 1869 Russian Chemist Dimitri Mendeleev (1834-1907) and German Chemist Lothar Meyer (1830-1885) 1869 Russian Chemist Dimitri Mendeleev (1834-1907) and German Chemist Lothar Meyer (1830-1885)

8. Nearly identical schemes for classifying Mendeleev given credit because published first Produced first periodic table Mendeleev given credit over Newlands because he sometimes broke the pattern to put in order of properties Allowed him to predict properties of missing elements Led to prediction of 2 elements not yet discovered

9. Mendeleev Mendeleev given credit because published first Produced first periodic table he sometimes broke the pattern to put in order of properties Allowed him to predict properties of missing elements Led to prediction of 2 elements not yet discovered

12. Mendeleev’s Prediction: B C N 10.8 12.0 14.0 Al Si P 26.7 28.0 30.9 Zn 65 Cd In Sn Sb 112.4 114.8 118.7 121.8 As 74.9 Eka Aluminum Eka Silicon

13. 1913 English Chemist H.G.J. Mosely Noticed that Mendeleev not always correct Arranged elements by atomic number, not mass

14. Periodic Law When elements are arranged in order of increasing atomic number, their physical and chemical properties show a periodic pattern