A new periodic table is designed to highlight the numbers of protons in a nucleus that make an atom most stable from a nuclear perspective, as opposed to the properties of the orbiting electrons that give rise to the chemical properties of an atom.
Over 150 years have passed since Dmitri Mendeleev discovered the periodic law that lead him to propose the classic periodic table. He even had the foresight to add space for elements that were still unknown in his time.
"Fundamentally, it comes down to the electrons in each atom. Atoms are considered to be stable when electrons completely fill their 'shell' of orbits around the nucleus," continues Maeno.
"So-called 'noble gases', inert elements such as helium, neon, and argon, rarely react with other elements. Their most stable electron numbers are 2, 10, 18, 36, and so on."
Maeno decribes these as atomic 'magic numbers', and importantly the same principle can also be applied to protons. Imagining that protons in a nucleus exist in 'orbits' may seem like a stretch, but the discovery of the concept was awarded the 1963 Nobel prize in physics.
Protons have different stable magic numbers: 2, 8, 20, 28, and so on. Among these are familiar elements such at helium, oxygen, and calcium. The Nucletouch table places these 'magic nuclei' at its center, providing a new perspective on the elements.
"Similar to electrons, when nuclear orbits are filled with protons, they form stable nuclei, analogous to the noble-gas elements," says collaborator Kouichi Hagino.
"In our nuclear periodic table, we also see that nuclei tend to be spherically-shaped near the magic numbers, but deformed as you move away from them."From a press release at Science Daily.
A nuclear periodic table based on the proton magic numbers. The rightmost column shows the elements with the proton magic and semi-magic numbers. The other elements are arranged according to the nuclear shell structure shown in Fig. 1, for which the single-particle levels for the valence protons are denoted with different colors. In the legend for the single-particle levels, those without j include both of the spin orbit partners, e.g. f for f5/2+f7/2. The elements shown in round-corner boxes are those whose nuclei are deformed in the ground state (see Möller et al. (Möller et al. 2016) for the actual values for the deformation parameter). Elements with black symbols have stable nuclei, while those with white symbols represent those with all the isotopes unstable. Even though Bi and Th are unstable, we do not include them in the unstable elements since their decay half-lives are of the order of the age of the universe or longer. Likewise, we do not include U in the unstable elements, since the half-life is similar to the age of the earth.
A nuclear periodic table similar to Fig. 2, but a version in which the elements are arranged symmetrically around the shell closures.
A paper model of the nuclear periodic table shown in Figs. 2 and 3. Corresponding to a similar model for the atomic periodic table known as “Elementouch” (Maeno 2002), we propose to call this model “Nucletouch”