Editing Chemical element (section)

=== Atomic number ===
{{main|Atomic number}}

The [[atomic number]] of an element is equal to the number of protons in each atom, and defines the element.<ref>{{cite web | url =http://www.ndt-ed.org/EducationResources/HighSchool/Radiography/atomicmassnumber.htm | title =Atomic Number and Mass Numbers | publisher =ndt-ed.org | access-date =17 February 2013 | archive-url =https://web.archive.org/web/20140212155836/http://www.ndt-ed.org/EducationResources/HighSchool/Radiography/atomicmassnumber.htm | archive-date =12 February 2014 | url-status =dead }}</ref> For example, all carbon atoms contain 6 protons in their [[atomic nucleus]]; so the atomic number of carbon is 6.<ref>{{cite web | url =http://periodic.lanl.gov/6.shtml | title =Periodic Table of Elements: LANL Carbon | author =periodic.lanl.gov | publisher =[[Los Alamos National Laboratory]] | access-date =17 February 2013 | archive-date =25 January 2021 | archive-url =https://web.archive.org/web/20210125032252/https://periodic.lanl.gov/6.shtml | url-status =live }}</ref> Carbon atoms may have different numbers of neutrons; atoms of the same element having different numbers of neutrons are known as [[isotope]]s of the element.<ref>{{cite web | url =http://faculty.piercecollege.edu/yamadak/classes/Atomic%20mass.pdf | title =Atomic mass, isotopes, and mass number. | author =Katsuya Yamada | publisher =[[Los Angeles Pierce College]] | url-status =dead | archive-url =https://web.archive.org/web/20140111131537/http://faculty.piercecollege.edu/yamadak/classes/Atomic%20mass.pdf | archive-date =11 January 2014 }}</ref>

The number of protons in the nucleus also determines its [[electric charge]], which in turn determines the number of [[electron]]s of the atom in its [[ionization|non-ionized]] state. The electrons are placed into [[atomic orbital]]s that determine the atom's [[chemical property|chemical properties]]. The number of neutrons in a nucleus usually has very little effect on an element's chemical properties; except for hydrogen (for which the [[kinetic isotope effect]] is significant). Thus, all carbon isotopes have nearly identical chemical properties because they all have six electrons, even though they may have 6 to 8 neutrons. That is why atomic number, rather than [[mass number]] or [[atomic weight]], is considered the identifying characteristic of an element.

The symbol for atomic number is ''Z''.