51 History of the Periodic Table

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5-1 History of the Periodic Table
Glenn Seaborg shows where the element named for
him is located on the periodic table of elements.
Element 106 Seaborgium (Sg)
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Stanislao Cannizzaro

• In 1860 presented a method for better determining
  atomic masses.

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Law of Octaves

• English chemist who in 1863 proposed the Law of
  Octaves which stated that chemical properties
  repeated with every eighth element.
• Because Newlands's use of a musical analogy in a
  chemical theory sounded like a regression to
  Pythagorean mysticism, the theory was ridiculed.

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Dmitri Mendeleev

• Organized the known elements into a table based
  on atomic mass and other properties.
• Credited with the periodic nature of the table.

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Mendeleevs Table - 1869

• Organized by increasing atomic mass
• Some elements out of sequence to preserve
  pattern.
• Left blanks to indicate elements not yet
  discovered.
• Periods vertical, groups horizontal

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Henry Moseley - 1911

• Moseleys work led to the discovery of the atomic
  number.
• Table rearranged by atomic number.
• Verified Mendeleev idea regarding out of sequence
  elements

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Gallipoli - 1915
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The Periodic Law

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

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Noble Gases

• Argon Strutt and Ramsay, 1894
• Helium (on Earth) 1895, Ramsay
• Krypton and Xenon Ramsay, 1898
• Radon Dorn, 1900
• Group 18

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Lanthanides

• 58 - 71
• Named for element 57 Lanthanum
• Very similar in properties

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Actinides

• 90 - 103
• Named for element 89 Actinium

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Periodicity

• As you move down a group periodicity in atomic
  number can be seen.
• For example in groups 1 and 18 the atomic number
  increases in a pattern of 8,8,18,18,32 as you
  move down the group.
• Periodicity is explained by electron
  configurations.

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