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How to Describe the Stability of an Atom Based on the Numbers of Protons and Neutrons

Elements are defined by their atomic numbers, which is equal to the number of protons/electrons, and their mass number, the whole number rounded from the atomic weight which equals the protons plus the neutrons. Isotopes are versions of elements that have differing numbers of neutrons; they retain the atomic number but not the atomic weight/mass number. Isotopes are labelled as being stable or unstable, with unstable elements prone to decay and degradation. While the exact nature of what makes an atom stable or unstable remains unknown, there are some general rules of thumb that make an atom more or less stable.

Instructions

- 1
  Determine the ratio of neutrons and protons (neutrons/protons) and check for how close the answer is to 1, noting that the smaller the atomic number of the element, the closer to 1 the answer needs to be. Mark anything higher than 1.518 automatically as being unstable as that's the ratio of the heaviest known isotope.
- 2
  Check whether the number of both protons and neutrons are even or if they are both odd. Atoms with even numbers of protons and neutrons are more stable than atoms with odd numbers of protons and neutrons.
- 3
  Determine if the number of protons and/or neutrons equals one of the so-called "magic numbers" of 2, 8, 20, 28, 50, 82 or 126. An atom with protons and neutrons equal to magic numbers are especially stable while those with only the protons or neutrons equal to a magic number are less stable (but still stable).

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