Answer;
-Because using letters was the easiest way to represent the elements. Also the use of chemical symbols is to allow them to write chemical formulas easily.
Step-by-step explanation;
-A chemical symbol is a shorthand method of representing an element. Instead of writing out the name of an element, we represent an element name with one or two letters. As you know, the periodic table is a chemist's easy reference guide.
-Chemical symbols are usually one or two letters long, but sometimes three letters are used. Every chemical symbol starts with a capital letter, with the second or third letters written in lower case.