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How to Figure the Atomic Mass of Isotopes

Every atom exists in several forms. One of the kinds of variation is due to changes within the nucleus. An atom is composed of electrons surrounding a core of protons and neutrons. Isotopes are atoms that have identical numbers of protons and electrons but a different number of neutrons in the nucleus. The atomic mass of an isotope is close to the sum of the mass of all its components, so it's not too difficult to calculate.

Instructions

- 1
  Find an isotope of interest. If you don't already have an isotope in mind, you can search through online resources, such as the Berkeley Laboratory Isotopes Project's Periodic Table of Isotopes.
  
  For example, you could pick the 16-neutron isotope of silicon.
- 2
  Find the atomic number of the isotope. The atomic number can be found directly from the periodic table. The atomic number is the same regardless of how many neutrons are in an isotope.
  
  For example, the atomic number of silicon is 14.
- 3
  Multiply the number of neutrons by the atomic mass of a neutron: 1.00728.
  
  For this silicon isotope, this would be 16 x 1.00728 = 16.11648.
- 4
  Multiply the atomic number by the atomic mass of a proton, 1.00866, and by the atomic mass of an electron: 0.00055.
  
  Again, for the example, this is 14 x 1.00866 = 14.12124; and 14 x 0.00055 = 0.00770.
- 5
  Add the masses calculated in Steps 3 and 4.
  
  For the example, this is 30.24542.

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