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  • 1. Chapter 5 History of the Periodic
  • 2. Chapter 5
  • 3. History of the Periodic Table The Periodic Law – Physical and Chemical Properties of Elements are Periodic Functions
  • 4. History of the Periodic Table The Periodic Law – Physical and Chemical Properties of Elements are Periodic Functions
  • 5. The development of the periodic table begins with German chemist Johann Dobereiner (1780-1849) who grouped elements based on similarities.
  • 6. Calcium (atomic mass 40), strontium (atomic mass 88), and barium (atomic mass 137) possess similar chemical properties. (Find them on the Periodic Table)
  • 7. Dobereiner noticed the atomic mass of strontium fell midway between the masses of calcium and barium: Ca Sr Ba 40 ?? 137 (40 + 137) ÷ 2 = ??
  • 8. Dobereiner noticed the same pattern for the alkali metal triad (Li/Na/K) and the halogen triad (Cl/Br/I). Li Na K Cl Br I 7 ?? 39 35 ?? 127
  • 9. (Was this merely a coincidence or did some pattern to the arrangement of the elements exist?)
  • 10. 1829 Dobereiner proposed the Law of Triads: The middle element in the triad had atomic mass that was the average of the other two members.
  • 11. 1829 Dobereiner proposed the Law of Triads: The middle element in the triad had atomic mass that was the average of the other two members.
  • 12. (Soon other scientists found chemical relationships extended beyond triads. Fluorine was added to Cl/Br/I group; sulfur, oxygen, selenium and tellurium were grouped into a family; nitrogen, phosphorus, arsenic, antimony, and bismuth were classified as another group.)
  • 13. First International Congress of Chemists Karlsruhe, Germany 1860 -to discuss uniform ways to measure Atomic Mass and to solve other communication problems. -Only 60 Elements at this time
  • 14. First International Congress of Chemists Karlsruhe, Germany 1860 -to discuss uniform ways to measure Atomic Mass and to solve other communication problems. -Only 60 Elements at this time
  • 15. Demetri Mendeleev 1869 FATHER OF THE MODERN PERIODIC TABLE Mendeleev insisted on ordering elements by atomic mass, and grouping them by their PROPERTIES.
  • 16. Demetri Mendeleev 1869 FATHER OF THE MODERN PERIODIC TABLE Mendeleev insisted on ordering elements by atomic mass, and grouping them by their PROPERTIES.
  • 17. Demetri Mendeleev 1869 FATHER OF THE MODERN PERIODIC TABLE Mendeleev insisted on ordering elements by atomic mass, and grouping them by their PROPERTIES.
  • 18. This resulted in several "gaps" in the Periodic Table. Both Gallium (Ga) and Germanium (Ge) were unknown at the time Thus there was a gap under Aluminum (Al) and a gap under Silicon (Si)
  • 19. Mendeleev concluded therefore that there must be two elements, which he called "eka-Aluminum" and "eka-Silicon" which must fill these gaps
  • 20. Mendeleev made predictions on some of the vacant spaces in the Periodic Table. Such as: Eka-silicon, (Germainium) Eka-aluminium, (Gallium)
  • 21. Gallium was discovered in 1875 by Paul Emile. Its general chemistry matched Mendeleev's predictions for
  • 22. Germanium (ekasilicon) was discovered in 1886 by Clemens Winkler. The agreement with Mendeleev's predictions are shown in the table below Property Ekasilicon Germanium 72 72.32 Density (g/cc) 5.5 5.47 Atomic volume 13 13.22 Atomic Mass Outer Shell Electrons (Dots) Boiling point of GeCl4 /degrees Celsius 4 4 <100 86
  • 23. Henry Moseley 1913 Assistant to Rutherford (killed at Gallipoli at age 28) -discovered a mathematical relationship between the frequency of X-rays and the atomic number.
  • 24. Henry Moseley 1913 Assistant to Rutherford (killed at Gallipoli at age 28) -discovered a mathematical relationship between the frequency of X-rays and the atomic number.
  • 25. He noticed that when struck by the cathode rays, different metals gave off x-rays with distinct wavelengths.
  • 26. Moseley realized that the atomic numbers were not just a convenient numbering scheme for the elements, but had a real physical meaning - ultimately realized as being the number of protons (and electrons) in an (neutral) element
  • 27. Law of Octaves (1837-1898), English chemist John Newlands having arranged the 62 known elements in order of increasing atomic masses, noted that at in intervals of eight, elements had similar physical/chemical properties.
  • 28. Newlands was the first to formulate the concept of periodicity in the properties of the chemical elements. In 1863 he wrote a paper proposing The Law of Octaves: Elements exhibit similar behavior to the eighth element following it in the table.
  • 29. Noble Gases 1864 He discovered on the Sun 1894 Englishman John Williams Strutt (Lord Rayleigh) and Scottish Sir William Ramsey discovered Argon 1895 He discovered on Earth 1898 Krypton and Xenon-Ramsey 1900 Radon discovered by German Friedrich Ernst Dorn