Relativistic Atoms

Last week I read a really interesting article in Scientific American about the periodic table, which, being a potential chemistry major (who happens to be able to recreate the periodic table from memory) immediately piqued my interest. Called “Cracks in the Periodic Table,” the article discussed how, as more elements are discovered beyond element 118 (the last element on the existing periodic table), the intrinsic order of the elements and their properties will begin to break down. I had heard something about this before, but had not been given an explanation for it. Apparently, this potential for the periodic table to “fail” in the future delves into the particle physics inside the atoms.

As atomic number of the elements increases, the numbers of protons and neutrons increases, thereby increasing the overall mass of the molecule. This causes the nucleus to be unstable, which we know as radioactivity, but also results in the electrons around the nucleus moving at a higher velocity. In atoms of lower atomic number elements, the velocity of the electrons really doesn’t have much of an effect on the element and its properties (as far as I know), but in the larger atoms, the increase in velocity results in the occurrence of some relativistic effects. The phenomenon known as electron shielding (which separates the energies of orbitals on the same electron sublevel) is lessened, making the electrons feel a stronger attraction to the nucleus and actually pulling all of the electrons closer, making the atomic radii smaller. The energies of electron orbitals are also affected.

These effects can actually already be seen in elements we understand quite well, like gold. Looking at the periodic table, almost all of the elements surrounding it, which it would be expected to share chemical and physical properties with, are a silverish color, but gold is, well, gold. I won’t get into all of the details of what’s happening, but basically a relativistic effect in gold causes atoms of the element to absorb a wavelength of blue light, making the metal appear yellowish to our eyes. In the other metals, this relativity is not felt, and they absorb wavelengths of ultraviolet light, which we cannot see, instead. I would not have expected that to be the reason for gold’s color, but its interesting.

In larger elements, the effects of relativistic electrons would be even greater, leading to a seeming disorder in elements that have yet to be added to the periodic table. Only time, and more research, while tell what those effects actually are.

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