Earth and moon

First posted on FB 17/01/2020

A pair of elements today, selenium and tellurium, adjacent in Group 16. 
Before Mendeleev proposed his Periodic Table, other scientists had put forward similar ideas. In 1862, Alexandre-Emile Beguyer de Chancourtois proposed a helical arrangement with the elements in order of relative atomic mass and those with similar properties aligned vertically. Tellurium was at the centre of this arrangement and so he called his arrangement the telluric screw – see the image below from the Science Museum’s collection.

Tellurium ore was discovered in Transylvanian mines in the late 18th century and was named for the Mother Earth from which it came, the Roman goddess Tellus (equivalent of the Greek Gaia). When selenium was discovered a little while later, and had similar chemical properties to tellurium, it was named after Selene, Greek Goddess of the Moon.

The observant among you will notice that this shows the phases of the moon as viewed from the Southern Hemisphere. I admit this wasn’t intentional and I had I thought about it before I was half way through I would probably have chosen to depict my northern perspective, but I think I can justify it by the fact that Brazil nuts are particularly rich in selenium, and are primarily grown south of the equator.…/model-of-the…

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