I knew that hydrogen was bIQSIp “water-gas”, and that made me think of German Wasserstoff “water-stuff”.
Then I saw that nitrogen was voQSIp “choke-gas”, and that made the impression even stronger; the German is Stickstoff “suffocate-stuff”. (Or so I presume. “To suffocate” is a prefixed form, ersticken, at least in modern German.)
So I guessed that oxygen might be peySIp “acid-gas”, to parallel German Sauerstoff “sour-stuff”. But alas! It’s yInSIp “life-gas” instead. A pity :)
It also made me think about the Greek roots: hydrogen is “water-producer” and oxygen is “acid-producer”. Nitrogen, though, is apparently “sodium carbonate producer”. Ah well.
For what it’s worth, Japanese element names parallel the German ones; this may be no coincidence, though, but rather due to calquing from German. (水素 suiso “water-element”, 酸素 sanso “acid-element”, 窒素 chisso “suffocate-element”.)
What other elements are there in Klingon?
There’s cha'puj “dilithium”… which makes me wonder whether element 3, lithium, might be puj or wa'puj :) And Qab “theragen” (found while searching for -gen words), but that’s a chemical compound, not a hypothetical element.
A brief search came up with nothing but the three above (H, N, O)—not even carbon or silicon, or the typical precious (on Earth) metals such as silver, gold, or platinum!