 the structural formula of a chemical compound is a graphic representation of the molecular structure, showing how the atoms are arranged. the chemical bonding within the molecule is also shown, either explicitly or implicitly. unlike chemical formulas, which have a limited number of symbols and are capable of only limited descriptive power, structural formulas provide a complete geometric representation of the molecular structure. for example, many chemical compounds exist in different isomeric forms, which have different enantiomeric structures but the same chemical formula. a structural formula is able to indicate arrangements of atoms in three dimensional space in a way that a chemical formula may not be able to do. several systematic chemical naming formats, as in chemical databases, may be are used that are equivalent to, and as powerful as, geometric structures. these chemical nomenclature systems include smiles, inchi and cml. these systematic chemical names can be converted to structural formulas and vice versa, but chemists nearly always describe a chemical reaction or synthesis using structural formulas rather than chemical names, because the structural formulas allow the chemist to visualize the molecules and the structural changes that occur in them during chemical reactions. == lewis structures ==   lewis structures (or "lewis dot structures") are flat graphical formulas that show atom connectivity and lone pair or unpaired electrons, but not three-dimensional structure. this notation is mostly used for small molecules. each line represents the two electrons of a single bond. two or three parallel lines between pairs of atoms represent double or triple bonds, respectively. alternatively, pairs of dots may be used to represent bonding pairs. in addition, all non-bonded electrons (paired or unpaired) and any formal charges on atoms are indicated. file:water-2d-flat.png|the lewis structure of water == condensed formulas == in early organic-chemistry publications, where use of graphics was strongly limited, a typographic system arose to describe organic structures in a line of text. although this system tends to be problematic in application to cyclic compounds, it remains a convenient way to represent simple structures: ch3ch2oh (ethanol) parentheses are used to indicate multiple identical groups, indicating attachment to the nearest non-hydrogen atom on the left when appearing within a formu
Chemical_formulas