Development of the Periodic Table

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  • Development of the Periodic Table
    • Early 1800s.
      • Scientists didn't know about atomic structure, including; protons, neutrons and electrons, and they had no atomic numbers.
      • All known elements were arranged in order of increasing relative atomic mass.
      • When this was done, a periodic pattern was noticed in the propertied of the elements, hence the name "periodic table".
      • Early periodic tables were incomplete, and some elements were placed in the wrong group.
        • This was because elements were placed in order of relative, without taking into account their properties.
    • Dmitri Mendellev
      • In 1869, Dmitri Mendeleev took 50 known elements and arranged them into his Table of Elements, leaving various gaps.
        • He put elements mostly in order of atomic mass, but did switch the order if the properties meant it should be changed.
      • Gaps were left in the table to ensure that elements with similar properties remained in the same groups.
        • Some of these gaps indicated the existence of undiscovered elements.
          • They allowed Mendeleev to predict what their properties may be.
          • When they were found and fitted the pattern, it helped to confirm Mendeleev's ideas.

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