In “periodic table”, the adjective is related to the noun period, and comes from Ancient Greek περίοδος through French périodique. In “periodic acid”, it is formed from the prefix per- and iodic (like peroxide and permanganate).

Wiktionary lists their respective UK pronunciations of as /pɪə(ɹ).iˈɒdɪk/ and /ˌpɜːraɪˈɒdɪk/, markedly different: pɪə (as in piece) vs. pɜː (as in perfume); then i (as in it) vs. (as in eye).

However, is that distinction really made in practice? Would a native US/UK/Aussie speaker make the difference when talking in the lab?

  • 3
    $\begingroup$ It only just occured to me that those words are written the same :) $\endgroup$
    – Mithoron
    Jul 31, 2015 at 13:39
  • 1
    $\begingroup$ I actually call periodic acid period acid just for fun ;D $\endgroup$
    – Jan
    Nov 8, 2017 at 12:52
  • $\begingroup$ Do you "read" books? I have "read" a few. $\endgroup$ Nov 8, 2017 at 13:29

3 Answers 3


I am an Australian English speaker and yes, this distinction is made in practice.

Possibly the only reasonable opportunity to use the pɪə pronunciation in the name of a compound is in the case of the entertaining molecule periodane, which is actually named after the periodic table. This molecule (and later a number of different plausible isomers) was identified computationally by a methodology called 'mindless chemistry' which optimises randomly generated molecular graphs. Periodane is a stable configuration of each atom on the second row of the periodic table, with the exception of neon (although some people are working on that).

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I'm not a professional chemist, just a student, but here are some observations from which I can speculate:

Note-- in this post,



(since IPA is annoying to read)

Remember, it's written as "per-iodic" acid many times. Which means it must be pronounced as "per-iodic" by whoever who reads/writes those texts. So we have some evidence showing the use of "per-iodic" as a pronunciation. I don't see any such evidence for "peer-iodic", though one of my teachers used it. I myself initially used "peer-iodic", but once I realized what the acid actually was, I switched to "per-iodic".


It is supposed to be pronounced as per-iodic acid schiff but there are many people who dont know that it contains iodine and call it peeriodic acid.


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