Dobereiner s triads

J. P. Montgomery, Dobereiner s Triads and Atomic Numbers, Journal of Chemical Education, 8-. 162-162, 1931. 

Montgomery, J. P, Dobereiner s triads and atomic numbers, J. Chem Educ,... 

Dobereiner s triads found a home in Mendeleyev s periodic table, published in 1872. Mendeleyev arranged the elements according to their relative weights, beginning with the lightest element, hydrogen (H). He placed elements with similar properties together vertically so that Dobereiner s triads appeared within Mendeleyev s periodic table. About... 

When the idea of relative atomic mass was first put forward, some chemists started to wonder whether there was a connection between the RAM of an element and its properties. One of these chemists, Dobereiner, in 1829, noticed that there were groups of three elements (triads) which had very similar chemical properties and in which the RAM of the middle element was almost exactly the average of the other two elements in the triad (these groups became knovm as Dobereiner s Triads). One triad was the three elements lithium, sodium and potassium all are soft metals, are highly reactive and have to be stored under oil. Their RAMs are lithium 7, sodium 23, potassium 39. As you can see, sodium s RAM is the average of 7 and 39. 

In the early 1800s, German chemist J. W. Dobereiner proposed that some elements could be classified into sets of three, called triads. Research and write a report on Dobereiner s triads. What elements comprised the triads How were the properties of elements within a triad similar ... 

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. 

Dobereiner s triads were useful because they grouped elements with similar properties and revealed an orderly pattern in some of their physical and chemical properties. The concept of triads suggested that the properties of an element are related to its atomic mass. 

In the following twenty-five years, other chemists expanded Dobereiner s triads and came out with groups of four or five related elements. 

In order to illustrate how KEY works, lets look at a specific example. In the 1820 s there were 50 or so elements that were known. While it was recognized that some elements were related, nobody had yet succeeded in ordering the elements in any sort of a periodic table. German scientist Johann Dobereiner made what is perhaps the first step towards such a classification. He pointed out that certain elements could be gathered into clusters of three based on similar chemical properties. The clusters (e.g., Cl-Br-I) became known as Dobereiner s triads ... 

For the rest of this account of the kingdom, however, we shall return to Earth and use the contemporary, well-thumbed chart of the kingdom that has been in our mind s eye all along and sprang from Dobereiner s triads, New-lands octaves, Odling s table, Meyer s rhythms, and Mendeleev s global insight. 

Dobereiner s triads /doh-ber-y-nerz/ Triads of chemically similar elements in which the central member, when placed in order of increasing relative atomic mass, has a relative atomic mass approximately equal to the average of the outer two. Other chemical and physical properties of the central member also lie between those of the first and last members of the triad. The German chemist Johann Wolfgang... 

Jerry Dias, a chemist at the University of Missouri—Kansas City, has devised a periodic classification of a class of organic molecules called benzenoid aromatic hydrocarbons, of which naphthalene, Cj Hg, is the simplest example (figure 1.10). By analogy with Johann Dobereiner s triads of elements, described in chapter 2, these molecules can be sorted into groups of three in which the central molecule has a total number of carbon and hydrogen atoms that is the mean of the flanking entries, both downward and across the table. This periodic scheme has been apphed to making a systematic study of the properties of benzenoid aromatic hydrocarbons, which has led to the predictions of the stabihty and reactivity of many of their isomers. 

Suffice it to say that Dobereiner s research estabhshed the notion of triads as a powerful concept, which several other chemists were soon to take up with much effect. Indeed, Dobereiner s triads, which would appear on the periodic table grouped in vertical columns, represented the first step in fitting the elements into a system that would account for their chemical properties and would reveal then-physical rektionships." ... 

And even further back in the story of the periodic system, one can see the influence of numerical approaches dating back to Prout s hypothesis and Dobereiner s triads, both of which predate the discovery of the periodic system. Hence, it is not just chemistry that enables one to classify the elements but a combination of chemistry with the urge to reduce, in the most general Pythagorean sense of describing facts mathematically. The story of the periodic system is the story of the blending of chemistry, Pythagoreanism, and most recently, quantum physics. 

Dobereiner s triads Groups of three chemically similar elements in which the... 

In 1829 the German chemist Johann Dobereiner (1780-1849) noticed that, where groups of three similar chemical elements occurred, the relative atomic mass of the middle element came about half-way between those of the other two. Two of Dobereiner s triads are shown in Figure 3.10. 

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