Naming a compound
Binary compounds are named n X 化 m E: the more electronegative element first, 化 “-ide”, then the other, with Chinese numerals for the counts. Salts drop the numerals, as in English. In 1871 the 化學鑑原 simply wrote the two element characters side by side, cation first, with small numerals for the atoms, which is why every element had to be a single character.
Today, covalent style
二氯化钙
Numerical prefixes as in “carbon monoxide”; the prefix of a single E is dropped.
Today, salt style
氯化钙
No prefixes: Cl-ide of Ca. Use 亞 before the metal for the lower oxidation state, 高 for a higher one.
1871, 化學鑑原
鈣緑氣 二
Cation first, then the anion character, atom counts as small numerals. Uses the 1871 characters where they differ from today's.
Elements: Ca and Cl. Electronegativity order decides which is X; unusual pairs may come out reversed.