Notation of one or two letters derived from the scientific names of the chemical element s (e.g., S for sulfur, Cl for chlorine, Zn for zinc).
Some hark back to Latin names: Au ( aurum ) for gold, Pb ( plumbum ) for lead. Others are named for people or places (e.g. einsteinium, Es, for Einstein). The present symbols express the system set out by the atomic theory of matter. Jons Jacob Berzelius gave many of the current names. Chemical formulas of {{link=compound">compound s are written as combinations of the elements' symbols, with numbers indicating their atomic proportions, using various conventions for ordering and grouping. Thus, sodium chloride is written as NaCl and sulfuric acid as H 2 SO 4 .