Chemical symbol

A chemical symbol is a one- or two-letter abbreviation that represents a chemical element. Its first letter is uppercase, and any second letter is lowercase.

Chemical element: A pure substance consisting of atoms with the same number of protons. Each chemical symbol names one element, distinguished by its atomic number.
Jöns Jacob Berzelius: A Swedish chemist who introduced the modern letter-based system of chemical symbols in the early nineteenth century. His notation established the system of element symbols still used today.
Chemical equation: A symbolic representation of a chemical reaction showing reactants, products, and their relative amounts. Element symbols let equations express reactions compactly and unambiguously.
Chemical symbol vs. chemical formula: The distinction between a single element abbreviation and a notation for the composition of a substance. A symbol names an element; a formula combines symbols to show composition.
Atomic number: The number of protons in an atom’s nucleus, which identifies its element. A symbol identifies an element whose defining property is its atomic number.
Alchemical symbol: A graphic sign used in alchemy to represent substances, processes, or celestial associations. Earlier chemical practice used pictorial signs rather than Berzelius’s letter abbreviations.
Isotope notation: A notation that identifies an isotope by placing its mass number and sometimes atomic number around an element symbol. The symbol can be extended with superscripts and subscripts to distinguish isotopes.
Chemical symbol vs. molecular formula: The distinction between an element abbreviation and a formula specifying the atoms in a molecule. Molecular formulas use element symbols but encode a molecule’s atom counts.
Chemical formula: A notation showing the elements in a substance and their relative numbers. Chemical symbols combine in formulas to represent compounds and elemental substances.
John Dalton: An English chemist whose atomic theory helped establish chemistry’s account of elements and compounds. Dalton’s atomic notation was an influential alternative before letter symbols prevailed.

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