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HISTORY OF THE PERIODIC TABLE. Johann Dobereiner. First noticed similarities among certain elements in 1829 Similar elements seemed to appear in groups of three Dobereiner’s Triads: ex. Cl, Br, I and Li, Na, K]. John Newland. - PowerPoint PPT Presentation
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First noticed similarities among certain elements in 1829
Similar elements seemed to appear in groups of three
Dobereiner’s Triads: ex. Cl, Br, I and Li, Na, K]
Arranged known elements in order of increasing atomic mass in 1864
Noticed similar chemical and physical properties
Newland’s Law of Octaves Problem: table had no gaps and
therefore left no room for new elements
Discovered periodic law in 1869 with Lothar Meyer but Mendeleev published his ideas first
Elements arranged in order of increasing atomic mass
Elements with similar properties recur at regular intervals
Gaps in the periodic table would later be filled by newly discovered elements (ie. Ga and Sc filled two of the gaps after they were discovered
Predicted properties of elements before they wer discovered
Caused periodic table to be modified by the discovery of Ar (noble gas) in 1894
Suggested in 1911 that the periodic table be arranged according to atomic number instead of atomic mass and thus eliminate several minor inconsistencies.
Example: according to atomic mass only, some elements appeared in the wrong column of the table, ie. Ar
In 1913, confirmed that the properties of elements depend on atomic number rather than atomic mass
RESULT: Our modern periodic table today
When elements are arranged in order of increasing atomic number, elements with similar chemical and physical properties occur at regular intervals.