Periodic table from Encyclopædia Britannica: https://www.britannica.com/science/periodic-table

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   John Carlos Baez (johncarlosbaez@mathstodon.xyz)'s status on Saturday, 01-Jun-2024 01:45:59 JST John Carlos Baez

   About half the periodic tables you see are wrong. The only question is: which half?

   Check out this one from Encyclopædia Britannica. See the row of elements in yellow-green near the bottom? They start with element 58, cerium and end with element 71, lutetium. There are 14 of them. They're called 'lanthanoids'.

   Okay. But note that lanthanum itself, element 57, is up somewhere else. It's *also* called a lanthanoid, and it's under two other elements in yellow-green called 'rare earths'.

   Next compare the periodic table on Wikipedia.

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