Why are some of the symbols on the periodic table of elements and others are not?

Answer 1

I've been trying for five minutes now to permute this into a question that actually makes sense, and this is the best I can come up with:

Sometimes, people use unofficial abbreviations, like "D" for deuterium or "Ph" for a phenolic group or "OAc" for acetate (particularly confusing one, that, as Ac is the symbol for actinium).

These don't appear on the Periodic Table because they aren't actually elements. Deuterium is an isotope of hydrogen, and the other two are polyatomic.

If that doesn't answer what you were trying to ask, please be a little more clear what symbols in particular you're talking about.

Answer 2

The symbols on the periodic table of elements are the abbreviated form of an element's name, often derived from its Latin name. Elements that were discovered earlier have symbols derived from their Latin names, while elements discovered later were given symbols based on their English names or alternate names. Symbols are chosen to represent an element in a concise and standardized way.