Isotopes

• All atoms of the same element have the same number of protons in the nucleus
• Atoms of the same element may have different numbers of neutrons in the nucleus
• Isotopes


  Atoms of the same element that have different numbers of neutrons
• Symbol for a specific isotope

  Mass number as a superscript to the left of the element symbol
• The atomic number is sometimes written as a subscript preceding the symbol, but since this number defines the element's identity, as does its symbol, it is often omitted