This section is from the book "Applied Science For Metal Workers", by William H. Dooley. Also available from Amazon: Applied Science For Metal Workers.
Elements cannot be decomposed by any known method or divided into anything simpler. The smallest particles of elements are known as atoms. Elements are sometimes found alone in the earth, as are pure copper and gold, but are usually associated with other elements. Nearly eighty elements have been discovered and named, but many of them are not commonly found. In chemistry, every elementary substance is represented by what is called a symbol, which is usually a single capital letter or one capital letter and one small letter. Symbols are used to save time in writing and to describe briefly and clearly the composition of a complicated compound substance.
Frequently the symbol for a substance is derived from the first or the first and second letters of the Latin term for the substance. For instance, Cu is the symbol for copper, and the Latin term from which it is derived is cuprum. In like manner, zinc, carbon, manganese, and silver are designated by the symbols, Zn, C, Mn, and Ag. Latin has furnished a number of the symbols for others of the common elements; thus, the symbol for sodium is Na (natrium), for potassium, K (kalium), and for iron, Fe (ferrum). The symbol Hg (hydrargyrum) for mercury is from the Greek.