History of the Periodic Table

In the early 1800s they could only use atomic mass
1. Categorisation through
  1. Physical and chemical properties
  2. Relative atomic mass
  3. No idea of atomic structure or protons/electrons
    Anmerkungen:
    - No such thing as atomic number - only in C21st after protons and electrons were discovered that it was realised that elements were best arranged in order of atomic number
2. Could only measure relative atomic mass - known elements arranged in order of atomic mass
Newlands' law of Octaves was the first good effort
1. Had the first good method of arranging in 1964
  Anmerkungen:
  - Noticed that every eighth element had similar properties, so listed some of the known elements in rows of sevens
  1. The sets of eight were called Newlands' Octaves
    Anmerkungen:
    - Unfortunately the pattern broke down on the third row - transition metals (Titanium Ti and Iron Fe) messed it up. He left no gaps so his work was ignored, but he was getting quite close
2. Criticised because...
  1. Groups contained elements that didn't have similar properties - eg. carbon and titanium
  2. Mixed up metals and non-metals - eg. oxygen and iron
  3. Didn't leave gaps for elements that haven't been discovered yet
Dmitri Mendeleev left gaps and predicted new elements
1. In 1869, Mendeleev from Russia had 50 known elements and arranged them with various gaps
2. Put his elements into order of atomic mass, but left gaps to keep elements with similar properties in the same vertical groups
3. The gaps were the clever bit as they predicted the properties of undiscovered elements - eventually found and fitted the pattern

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History of the Periodic Table

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