The atomic number of an element, which indicates its place in the periodic table of elements, is the number of protons (positively charged particles) in the nucleus of one of its atoms. If an atom is electrically neutral, the same number of electrons are present. Atomic number is often symbolized with the letter Z and is shown as a numerical subscript to the left of its chemical symbol. For example, the letter C preceded by a superscript number 12 and a subscript number 6 indicates a carbon atom of atomic mass 12 and atomic number 6, the difference being equal to the number of neutrons present in the nucleus.

See Nucleus.