numerous rectangular variations, other periodic table formats have included, for example, [ n 8 ] circular, cubic, cylindrical, edificial (building-like), helical, lemniscate , octagonal prismatic, pyramidal, separated, spherical, spiral, and triangular forms. Such alternatives are often developed to highlight or emphasize chemical or physical properties of the elements that are not as apparent in traditional periodic tables. [ 81 ] A popular [ 82 ] alternative layout is that of Theodor Benfey (1960). The elements are arranged in a continuous spiral, with hydrogen at the center and the transition metals, lanthanides, and actinides occupying peninsulas. [ 83 ] The various forms of periodic tables can be thought of as lying on a chemistry–physics continuum. [ 90 ] Towards the chemistry end of the continuum can be found, as an example, Rayner-Canham's 'unruly' [ 91 ] Inorganic Chemist's Periodic Table (2002), [ 92 ] which emphasizes trends and patterns, and unusual chemical relationships and properties. Near the physics end of the continuum is Janet's Left-Step Periodic Table (1928). This has a structure which shows a closer connection to the order of electron-shell filling and, by association, quantum mechanics . [ 93 ] Somewhere in the middle of the continuum is the ubiquitous common or standard form of periodic table. This is regarded as better expressing empirical trends in physical state, electrical and thermal conductivity, and oxidation numbers, and other properties easily inferred from traditional techniques of the chemical laboratory. [ 94 ] This form of periodic table is more congruent with