What is the rule in assigning kanji to a new word?


For example, Hydrogen was found by Henry Cavendish. Mr. Cavendish was not a
Japanese and I'm pretty sure he won't bother inventing the name for Hydrogen
in all the languages in the world, especially in a language that doesn't use
the same set of alphabet as the languages he mastered. In fact, he didn't even
name it. It was Antoine Lavoisier who gave the name Hydrogen. Google translate
translates Hydrogen as 水素 (すいそ).

What I want to know is how the kanji 水素 was chosen to represent Hydrogen? What
are the rules that one must follow in assigning kanji to a newly found
thing/word? Or one can just assign whatever kanji he wants much like how in
English you can just assign whatever name you want to something you found,
like is the case with Big Bang being named Big Bang even when it is not an
explosion.




See this article: [Chemical elements in East Asian
languages](https://en.wikipedia.org/wiki/Chemical_elements_in_East_Asian_languages)

In general, Japanese experts today no longer create totally new kanji
compounds. They use kanji only when a combination of existing compounds
(words) can directly represent the original phrase. For example, _deep
learning_ is translated either as ディープ・ラーニング or 深層学習, where 深層 ("depth") and
学習 ("learning") are both very old words.

Old Japanese people (approx. 100-150 years ago) tended to create various new
kanji compounds based on the characters' meanings, as they rapidly learned
many Western concepts. Examples include 文明 ("literacy" + "enlightenment" =
"civilization"), 電話 ("electricity" + "talk" = "phone"), 物理 ("thing" + "reason"
= "physics"), 野球 ("field" + "ball" = "baseball"). Some of these new words were
actually reverse-imported to Chinese. See [wasei-
kango](https://en.wikipedia.org/wiki/Wasei-kango). I don't believe there is a
technical term that was assigned purely random kanji in those days.

Some traditional chemical element names such as 水素/臭素 were created in the same
manner ("water" + "element" = "hydrogen", "stench" + "element" = "bromine"). I
think the etymology of 水素 is fairly straightforward. However, chemical
elements discovered relatively recently are simply transliterated using
katakana. For example, Neptunium is translated as ネプツニウム in Japanese. On the
other hand, Chinese people still keep inventing new compounds for new Western
names/concepts (See
[this](https://chinese.stackexchange.com/questions/242/how-do-we-choose-the-
correct-characters-for-a-westerner-name) and
[this](https://japanese.stackexchange.com/q/23557/5010)). They are even
inventing a new kanji for each new chemical element (Neptunium is 镎 in
Chinese).




See this article: [Chemical elements in East Asian
languages](https://en.wikipedia.org/wiki/Chemical_elements_in_East_Asian_languages)

In general, Japanese experts today no longer create totally new kanji
compounds. They use kanji only when a combination of existing compounds
(words) can directly represent the original phrase. For example, _deep
learning_ is translated either as ディープ・ラーニング or 深層学習, where 深層 ("depth") and
学習 ("learning") are both very old words.

Old Japanese people (approx. 100-150 years ago) tended to create various new
kanji compounds based on the characters' meanings, as they rapidly learned
many Western concepts. Examples include 文明 ("literacy" + "enlightenment" =
"civilization"), 電話 ("electricity" + "talk" = "phone"), 物理 ("thing" + "reason"
= "physics"), 野球 ("field" + "ball" = "baseball"). Some of these new words were
actually reverse-imported to Chinese. See [wasei-
kango](https://en.wikipedia.org/wiki/Wasei-kango). I don't believe there is a
technical term that was assigned purely random kanji in those days.

Some traditional chemical element names such as 水素/臭素 were created in the same
manner ("water" + "element" = "hydrogen", "stench" + "element" = "bromine"). I
think the etymology of 水素 is fairly straightforward. However, chemical
elements discovered relatively recently are simply transliterated using
katakana. For example, Neptunium is translated as ネプツニウム in Japanese. On the
other hand, Chinese people still keep inventing new compounds for new Western
names/concepts (See
[this](https://chinese.stackexchange.com/questions/242/how-do-we-choose-the-
correct-characters-for-a-westerner-name) and
[this](https://japanese.stackexchange.com/q/23557/5010)). They are even
inventing a new kanji for each new chemical element (Neptunium is 镎 in
Chinese).

