{"term":{"id":"02282","title":"extent","longtitle":"IUPAC Gold Book - extent","doi":"10.1351\/goldbook.E02282","code":"E02282","status":"current","also defines":"<em>also defines<\/em>: geometric surface area, stepped surface, real surface area","mentioned":"<em>mentioned<\/em>: geometric interface area","definitions":[{"id":1,"text":"A quantity measured by its area, \\(A\\) (or \\(S\\)). For solids, a real (true, actual) and a geometric surface (interface) area, \\(A_{\\rm{r}}\\) and \\(A_{\\rm{g}}\\), respectively, may be defined if asperities are present whose height is orders of magnitude greater than the atomic or molecular size. The geometric surface is the projection of the real surface on a plane parallel to the macroscopic, visible phase boundary. If asperities are of the order of the atomic size, the surface of the solid may be described as stepped. (High index faces of crystals are stepped surfaces but may be ideally smooth in the sense of the roughness factor.)","contexts":[],"links":[{"term":"roughness factor","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/R05419"},{"term":"visible","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/VT07496"}],"sources":["PAC, 1986, 58, 437. 'Interphases in systems of conducting phases (Recommendations 1985)' on page 439 (https:\/\/doi.org\/10.1351\/pac198658030437)"]}],"altoutputs":{"html":"https:\/\/goldbook.iupac.org\/terms\/view\/E02282\/html","xml":"https:\/\/goldbook.iupac.org\/terms\/view\/E02282\/xml","plain":"https:\/\/goldbook.iupac.org\/terms\/view\/E02282\/plain"},"citation":"Citation: 'extent' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351\/goldbook.E02282","license":"The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0\/) for individual terms.","collection":"If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org .","disclaimer":"The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.","accessed":"2026-05-06T03:36:52+00:00"}}