The atomic number is typically located at the bottom left or the top left corner of the isotope symbol. The isotope symbol is written in the form:
Element symbol−Mass number ext{{Element symbol}} - ext{{Mass number}}Element symbol−Mass number or Element symbol−Atomic number ext{{Element symbol}} - ext{{Atomic number}}Element symbol−Atomic number
The mass number is the sum of protons and neutrons in the nucleus of an atom, while the atomic number represents the number of protons in the nucleus. In the isotope symbol, the atomic number is often written as a subscript to the left of the element symbol or as a superscript above the element symbol. For example:
Carbon-12:prescript126C ext{{Carbon-12}}: quad prescript{12}{6}{ ext{C}}Carbon-12:prescript126C Hydrogen-1:prescript11H ext{{Hydrogen-1}}: quad prescript{1}{1}{ ext{H}}Hydrogen-1:prescript11H Oxygen-18:prescript188O ext{{Oxygen-18}}: quad prescript{18}{8}{ ext{O}}Oxygen-18:prescript188O
In these examples, the atomic numbers are represented by the subscripts 6, 1, and 8, respectively.