| Early periodic tables |
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| • | 1817: Döbreiner's triads – 3 elements w/
regularly |
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| varying
properties: S Se Te |
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| • | 1865: Newlands – "law of octaves",
about 55 |
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| elements |
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| • | Early tables were
based on mass number (A) or |
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| “combining
weight” |
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