According to ChemWiki at the University of California, Davis, a nuclide denotes a specific atomic nucleus of a chemical element. Nuclides are represented using a nuclide symbol, which consists of the element symbol, the mass number, the atomic number and an optional charge.
The mass number A is the number of protons and neutrons in the nucleus. It is written as a superscript to the left of the symbol of the chemical element. The atomic number Z is the number of protons and is denoted at the bottom left of the chemical symbol. A nuclide may also represent positive or negative ions. In this case, the charge is written at the top right of the element symbol.