Protactinium – element 91 but my 100th element stitched! Not all have been posted so far, but this milestone means that I have just lanthanum and actinium left in the f-block before moving on up the s-block to top it off with hydrogen. Then it’s decision time on Group 3 – where to place scandium and yttrium – before my final element, oganesson.
I must admit I really struggled to find a pattern to represent protactinium. The information accompanying RSC’s Periodic Table states ‘Protactinium is little used outside of research.’ and ‘Protactinium has no known biological role.’ It has no entry in the indexes of most of the books I have referred to so far, nor in my new favourite book: Philip Ball’s The Elements – a Visual History of their Discovery. The best I got was a passing mention in Kit Chapman’s Superheavy where it was mentioned as being one of the elements either side of thorium.
Even it’s name is barely its own, referring to another element: it means precursor to actinium. But it is the name that eventually led me to a pattern. Protactinium was discovered in 1917 by Lise Meitner and Otto Hahn, and named by Meitner because of its place in the decay chain of actinium: it is formed by beta decay of thorium and decays by alpha decay to actinium. The chain starts with uranium at the top left, zig-zagging its way down to lead bottom right. Protactinium is stitched in double thread.