Dmitri Mendeleev’s detailed prediction in 1871 of the properties of three as yet unknown elements earned him enormous prestige. Eleven other predictions, thrown off without elaboration, were less uniformly successful, thanks mainly his unbending adherence to the structure of his table and his failure to account for the lanthanides. At the end of his life he returned to his table without making the required changes, and added a theoretical discussion of elements lighter than hydrogen. The overall balance of success and (...) failure is nevertheless in his favour. There may now be a similar failure to understand the ultra-heavy elements because of adherence to the pattern of chemical groups. (shrink)

The s, p, d and f blocks of the elements, as delimited by Charles Janet in 1928, can be represented as parallel slices of a regular tetrahedron. They also fit neatly on to the surface of a sphere. The reasons for this are discussed and the possible objections examined. An attempt is made to see whether there are philosophical implications of this unexpected geometrical regularity. A new tetrahedral design in transparent plastic is presented.

The first attempt to represent the Periodic system graphically was the Telluric Helix presented in 1862 by Alexandre-Emile Béguyer de Chancourtois, in which the sequence of elements was wound round a cylinder. This has hardly been attempted since, because the intervals between periodic returns vary in length from 2 to 32 elements, but Charles Janet presented a model wound round four nested cylinders. The rows in Janet’s table are defined by a constant sum of the first two quantum numbers, n (...) and l, so that they end with the s-block, headed by hydrogen and helium. By combining Janet’s table, Edward Mazurs’ version, in which each row represents an electron shell and Valery Tsimmerman’s use of a half square for each element, I have produced a representation that can be printed out and wound round to make a cylinder with manageable dimensions. In the unwound version, I have placed the s-block in the middle, to emphasise its pivotal nature, since it both ends each row and contributes electrons to the valence of elements in the next row; it thus does not necessarily belong either on the left or the right side of a table. The downward arrows that link subshells within each series graphically illustrate the Janet Effect. To acknowledge my debt to Chancourtois, Janet, Mazurs and Tsimmerman, I call my design the ‘Telluric Remix’. (shrink)

Mendeleev’s successful predictions were the fruit of his insight into the structure of the periodic system. His failures were the result of pursuing the pattern he had perceived beyond the limits of its applicability. These two things are not equivalent.

Mendeleev’s successful predictions were the fruit of his insight into the structure of the periodic system. His failures were the result of pursuing the pattern he had perceived beyond the limits of its applicability. These two things are not equivalent.

Janet is known almost exclusively for his left-step periodic table (LSPT). A study of his writings shows him to have been a highly creative thinker and a brilliant draftsman. His approach was primarily arithmetic-geometric, but it led him to anticipate the discovery of deuterium, helium-3, transuranian elements, antimatter and energy from nuclear fusion. He recognized the (n + ℓ) rule well before Madelung and correctly placed the actinides. His controversial treatment of helium at the head of the alkaline earth elements (...) might be less provocative if his system were taken in one of its spiral representations. (shrink)

Mendeleev’s failure to represent the periodic system as a continuum may have hidden from him the space for the noble gases. A spiral format might have revealed the significance of the wide gaps in atomic mass between his rows. Tables overemphasize the division of the sequence into ‘periods’ and blocks. Not only do spirals express the continuity; in addition they are more attractive visually. They also facilitate a new placing for hydrogen and the introduction of an ‘element of atomic number (...) zero’. (shrink)