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Organizing the Elements

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					Organizing the Elements
      The Periodic Table
               Early Greeks
 Four classical
  elements: earth,
  water, wind, and fire.
 Correspond with solid,
  liquid, gas, and
  plasma.
                  Elements

 A few elements have been known for thousands
  of years: copper, silver, and gold.
 Only 13 elements were discovered by the year
  1700.
 When chemists started using the scientific
  method, the rate increased to finding 5 new
  elements in 10 years.
 Chemists needed a way to organize the
  elements- used the properties of the elements to
  sort them into groups.
J.W. Dobereiner (1780-1849)
German Chemist
   Published a classification
    system where elements
    were put into triads.
   A triad is a group of 3
    elements with similar
    properties.
   An example of on such
    triad is chlorine, bromine,
    and iodine.
Chlorine, Bromine, and Iodine



                   Liquid Bromine




   Chlorine Gas

                        Iodine
    Chlorine, Bromine and Iodine
 Look different or have different physical
  properties.
 Have similar chemical properties.
     -all react easily with metals.
 The average atomic masses of chlorine
  and iodine is 81.177 amu. This is close to
  bromine which is in the middle of the
  other two.
          Dmitri Mendeleev
 Russian chemist in
  1869 who published a
  chart of elements
 Arranged the
  elements in order of
  increasing atomic
  mass
    Mendeleev’s Periodic Table
 Mendeleev put
  question marks where
  he predicted elements
  should be.
 He predicted their
  properties as well as
  their position on the
  periodic table.
              Henry Moseley
 1913, determined an
  atomic number for
  each element
 Helped arrange the
  periodic table in order
  of increasing atomic
  number.
               Periodic Law
   When elements are arranged in order of
    increasing atomic number, there is a periodic
    repetition of their physical and chemical
    properties.
        Summary Questions
 What are the 4 classical elements? (early
  greeks)
 Who was the first to try and arrange a
  periodic table?
 How did Mendeleev’s periodic table differ
  from the modern periodic table?
 What did Henry Moseley contribute to the
  periodic table?

				
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posted:2/17/2013
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