relative atomic mass

• Relative atomic mass of an element is the mean mass of the isotopes of an element compared to 1/12 of the of the mass of a carbon-12 atom.
• One isotope has a mass of 35 with a relative abundance of 75%, the other has a mass of 37 with a relative abundance of 25%.

  Ar = (35 x 75) + (37 x 25)     =   35.5

                   (75+25)