Law of Triads

He called this the Law of Triads . This encouraged other scientists to search for patterns. 

In 1829 German chemist Johann Dobereiner noted that there were triplets of elements in which the central species properties were almost exactly midway between the outer two. The first example of such a triplet included chlorine, bromine, and iodine. Properties such as atomic weights, color, and reactivity followed this law of triads for several such groupings, but not for the entire collection of known elements. 

Dobereiner showed (mentioning Dalton) that atmospheric air is not a compound. He pointed out that the equivalent of strontiiun (42 5) is the arithmetic mean of those of calcium (20) and barium (65), and in 1829 he extended this relation (afterwards called the law of triads ) to many other groups of three analogous elements ( Trias ). In 1817 he pointed out that widely distributed elements have small atomic weights (stoichiometric numbers), and that some elements (Fe, Co, Ni, Cr, Mn) have nearly the same atomic weights. He established the identity of chromic acid, which had been questioned by... 

The development of the periodic table took many years and involved many scientists from different countries building upon the foundations of each other s work and ideas. The first attempts to categorize the elements were by Dobereiner ( law of triads ) and Newlands ( law of octaves ). Mendeleev was the first chemist to devise a periodic table with all the known elements that he used to predict properties of undiscovered elements. Mendeleev s periodic table has been modified in the light of work carried out by Rutherford and Moseley. Discoveries about sub-atomic properties led them to realise that elements should be arranged by atomic number. 

T1.2 Your coverage of early proposals for the periodic table should at least include DObereiner s triads, Newlands Law of Octaves, and Meyer s and Mendeleev s tables. From the modem designs (post-Mendeleev) you should consider Hinrichs spiral periodic table, Benfey s oval table. Janet s left-step periodic table, and Dufour s Periodic Tree. 

Figure 3.40 Julius Lothar Mayer (1830-1895), who pointed out that triads of elements, such as lithium, sodium, and potassium, and magnesium, calcium, and strontium, had similar chemical properties. He independently formulated the periodic law of the elements at about the same time as Mendeleev. (Published with permission from the Deutsches Museum, Munich.)...

Cobalt, in its properties, is an excellent intermediary between iron and nickel, and, moreover, it is clearly a suitable element to constitute the first of the central vertical triads of Group VIII, namely, Co, Eh, and Ir. Hence, if the Periodic Law holds absolutely, the atomic weight of cobalt should exceed that of iron, but not that of nickel. Either, therefore, the atomic weight of cobalt is slightly too high or that of nickel is slightly too low. 

Human society, the maintenance of which has always required the proper manipulation of the brains of its members, is still in development. It seeks its final equilibrium This will be the state reached when the modification of behavior induced by the triad offamily/school/society is based from birth until death on the exact knowledge of the natural laws that keep the brain and its self going. 

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