Explain why some symbols - for example, Cl and Si - have two letters
Answers
Answer:
You might think that the earliest elements might have been called by their initial until a second one turned up with the same initial, necessitating a second letter to distinguish them. That’s not how it went, though. Copper (Cu: Latin cuprum) was named before carbon (C), and iron (Fe: ferrum) before fluorine (F). Uranium is quite a latecomer but scores a single letter, U. What’s more, it’s the only U element. There is only one X element too, xenon, but that gets a second letter: Xe. Argon (for a long time A) was identified much more recently than gold (Au: aurum). Argon (A) has since 1957 been Ar. I don’t honestly know why! Likewise I don’t know the answer to your question, except to quote tradition, the resource of the destitute. Except that doesn't help either.
There is no longer an element A, so it joins the spare solitary letters, E, G, L, M, R, V, X, Y and Z. J and Q don’t count: no elements start with those letters. D and T exist, but they are isotopes of H (hydrogen) so are not separate elements at all. There is no rhyme or reason that I have been able to find.