Johann proposed "Law of Triads"- triads (3) of elements- middle element- average of outside ones (19h 40min, jan 2, 1829 y – 21h 30min, jan 1, 1830 y)
Description:
Halogen Triad- Chlorine, Bromine, Iodine
Alkali Metal Triad- Lithium, Sodium, Potassium
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History of the Periodic Table
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