Title: atomic charge
Long Title: IUPAC Gold Book - atomic charge
DOI: 10.1351/goldbook.AT06994
Status: current

Definition
The charge attributed to an atom \(A\) within a molecule defined as \(\zeta =Z_{\rm{A}}- q_{\rm{A}}\), where \(Z_{\rm{A}}\) is the atomic number of \(A\) and \(q_{\rm{A}}\) is the electron density assigned to \(A\). The method of calculation of \(q_{\rm{A}}\) depends on the choice of the scheme of partitioning electron density. In the framework of the Mulliken population analysis \(q_{\rm{A}}\) is associated with the so-called gross atomic population: \(q_{\rm{A}}=\sum q_{\unicode[Times]{x3BC}}\), where \(q_{\unicode[Times]{x3BC}}\) is a gross population for an orbital \(\unicode[Times]{x3BC}\) in the basis set employed defined according to \[q_{\unicode[Times]{x3BC}} = P_{\unicode[Times]{x3BC}\unicode[Times]{x3BC}}+\sum _{\begin{array}{c}
\nu \neq \unicode[Times]{x3BC} 
\end{array}}P_{\unicode[Times]{x3BC}\nu}\ S_{\unicode[Times]{x3BC}\nu}\] where \(P_{\unicode[Times]{x3BC}\unicode[Times]{x3BD} }\) and \(S_{\unicode[Times]{x3BC}\unicode[Times]{x3BD}}\) are the elements of density matrix and overlap matrix, respectively (see overlap integral). In the Hückel molecular orbital theory (where \(S_{\unicode[Times]{x3BC}\nu} = \delta _{\unicode[Times]{x3BC}\nu}\)), \(q_{\unicode[Times]{x3BC}} = n_{\unicode[Times]{x3BC}}\ P_{\unicode[Times]{x3BC}\unicode[Times]{x3BC}}\), where \(n_{\unicode[Times]{x3BC}}\) is the number of electrons in the \(\rm{MO}\,\unicode[Times]{x3BC}\).

Related Terms
- atomic number: https://goldbook.iupac.org//terms/view/A00499
- basis set: https://goldbook.iupac.org//terms/view/BT06999
- electron density: https://goldbook.iupac.org//terms/view/E01986
- molecular orbital: https://goldbook.iupac.org//terms/view/M03996
- overlap integral: https://goldbook.iupac.org//terms/view/O04357

Source
- PAC, 1999, 71, 1919. 'Glossary of terms used in theoretical organic chemistry' on page 1924 (https://doi.org/10.1351/pac199971101919)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/AT06994/html
- json: https://goldbook.iupac.org/terms/view/AT06994/json
- xml: https://goldbook.iupac.org/terms/view/AT06994/xml

Citation: Citation: 'atomic charge' 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.AT06994
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: 2026-06-21T05:54:51+00:00