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Argon but not forgotten

...elements from my Chemistry O Level coming back to me.

It started with my daughter's chemistry homework.  "Do you know anything about Sodium?" she asked.  "Na..." I replied, having waited years for an opportunity to crack that joke (which I then had to explain).

I tweeted it and a friend tweeted back: "ArF" which I thought was just a sarcastic laugh with an accidentally capitalised F.  But it turned out this was another chemistry joke, because ArF is the formula for the compound Argon Fluoride, which is used in specialist lasers.

Hang on, I thought, Argon is one of the so-called noble gases which don't react with anything. It gets its name from the greek word argos meaning lazy, because Argon doesn't do anything.  

Well apparently it's been known for 50 years or more that the inert gases aren't entirely inert at all, with Xenon and Krypton being quite happy to react with Fluorine, for example.  Our chemistry teacher lied to us, or at least the syllabus did.

Anyway, this gave me a chance to teach my daughter one of my favourite mnemonics, the one for learning the first nine elements in the periodic table:

        Hippety Hop Little Benjamin Bunny Can Never Overtake Flopsy

                             (H  He  Li  Be B C N O F)

Finally, here's a cryptic, if not Kryptonic, puzzle on this theme:  

Helium Neon Nitogen Krypton Xenon Radon.  Explain.

The typo is deliberate, by the way.




Answer: Argon ....the 'r' is gon in Nit(r)ogen....variant of a puzzle I first heard from David Bodycombe I think.