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2019 has been designated the International Year of the Periodic Table as it is the 150th Anniversary of the formulation of Mendeleev's Tabelle I

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1920

Stewart's Arrangement of The Elements

From A.W. Stewart, Recent Advances in Physical and Inorganic Chemistry, 3rd ed., Longmans, Green and Co., London (1920) 

René Vernon writes:

"Stewart discusses the 'forced symmetry' of Mendeleev's table, and the distinction between 'facetious symmetry' (as he calls it) and the actual correlation of facts (as he saw them at that time)."

Extracts:

237. Mendeleev... objected strongly to the employment of graphic methods of expressing the Periodic Law, on the ground that such methods did not indicate the existence of a limited and definite number of elements in each period.

239. The Periodic Table, as laid down by Mendeleeff in his writings, exhibits a symmetry which was one of its greatest assets. For some psychological reason, symmetry has an attraction for the human mind; and we are always apt to prefer a regular arrangement to one in which irregularities pre- dominate. Psychological peculiarities are, however, undesirable guides in the search for truth; and a careful examination of the Table in the light of our present knowledge will suffice to show that it can boast of no such symmetry as we are led to expect from the text-books of our student days.

For example, owing to the omission of some of the rare earth elements and by the insertion of blanks, the Table in its original form attained a very high degree of regularity; but since there are, as we know from the X-ray spectra results, only sixteen elements to fill the eighteen vacant spaces in the Table, it is evident that the symmetry of Mendeleeff s system is purely factitious.

Further, in order to produce the appearance of symmetry, Mendeleeff was forced to place copper, silver, and gold in the first group, although there is no known oxide Au2O and the stable chloride of gold is AuCl3.

These examples are well-known, and are mentioned here only for the purpose of enforcing the statement that the symmetry of Mendeleef's system cannot be sustained at the present day. Fascinating though its cut-and-dried regularity may be, we cannot afford to let symmetry dominate our minds when in actual fact there is no symmetry to be found.

240. The most superficial examination shows that, instead of being a symmetrical whole, the Table is really pieced together from a series of discrete sections.

250. The first attempt to arrange all the elements in a periodic grouping took the form of a three-dimensional model the Telluric Helix of de Chancourtois and it is not surprising that from time to time attempts have been made to utilize the third dimension as an aid to classification. It cannot be said that much light has been thrown on the matter by these essays; but some account of them must be given here for the sake of completeness.

251. The main drawback to the spiral representation appears to be that in it no new facts are brought to light, and there is no fresh collocation of the allied elements which might give it an advantage over the ordinary forms of classification. Also, in most cases it is more difficult to grasp as a whole.

253 ...if we have to choose between factitious symmetry and actual correlation of facts, we must decide in favour of the latter, discomforting though the choice may be.

255. The following new grouping seems worth considering. Although it has many good points, it is not to be regarded as a final solution, but is put forward mainly in the hope that an examination of it may suggest some more perfect system.

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© Mark R. Leach 1999-


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