Adv. Chem

• More than 60 elements had been discovered


  1860
• A group of chemists assembled at the First National Congress of Chemists in Karlsruhe, Germany, to settle the issue of atomic mass as well as some other matters

  September 1860
• Stanislao Cannizzaro


  An Italian chemist who presented a convincing method for accurately measuring the relative masses of atoms
• Cannizzaro's method enabled chemists to agree on standard values for atomic mass and initiated a search for relationships between atomic mass and other properties of the elements
• Dmitri Mendeleev


  A Russian chemist who noticed that when the elements were arranged in order of increasing atomic mass, certain similarities in their chemical properties appeared at regular intervals
• Mendeleev's creation of the periodic table

  1. Arranged elements with similar properties together

  2. Published first periodic table in 1869

  3. Discovered the periodic law
• All 3 elements (Scandium, Gallium, Germanium) had been discovered

  1886
• Henry Moseley


  An English scientist, working with Ernest Rutherford, who examined the spectra of 38 different metals
• Moseley's work led to the modern definition of atomic number, not atomic mass, as the basis for the organization of the periodic table
• Periodic Law


  The physical and chemical properties of the elements are periodic functions of their atomic numbers
• Periodic Table


  An arrangement of the elements in order of their atomic numbers so that elements with similar properties fall in the same column, or group
• Noble Gases


  • Most significant addition to the periodic table
  • Discovered by John William Strutt (Lord Rayleigh) and William Ramsay
  • Argon (Ar) discovered in 1894 as a gas in the atmosphere that had previously escaped notice because of its total lack of chemical reactivity
  • Helium (He) discovered in 1868 as a component of the Sun, and shown to also exist on Earth in 1895
  • Krypton (Kr) and Xenon (Xe) discovered in 1898
  • Radon (Rn) discovered in 1900 by the German scientist Friedrich Ernst Dorn
• Groups in the Periodic Table

  • Group 17 - Fluorine Family
  • Group 1 - Lithium Family
• Lanthanides


  The 14 elements with atomic numbers from 58 (Cerium, Ce) to 71 (Lutetium, Lu)
• Actinides


  The 14 elements with atomic numbers from 90 (Thorium, Th) to 103 (Lawrencium, Lr)
• Lanthanides and Actinides belong in Period 6 and 7, respectively, of the periodic table between the elements of Group 4
• Lanthanides and Actinides are usually set off below the main portion of the periodic table
• Periodicity with respect to atomic number can be observed in any group of elements in the periodic table
• Differences between atomic numbers of successive elements in groups

  • Group 1: 3, 8, 19, 37, 55
  • Group 18: 2, 8, 18, 36, 54
  • Group 2 and 13-17 follow a similar pattern