numéro de masse

Traductions

• anglais

  Date : 1987

  Définition

  A whole number representing the total number of protons and neutrons in a given atomic nucleus; it should not be confused with atomic number, which is the number of protons only.
  
  The sum of the neutrons and protons in a nucleus.

  Notes :

  For exemple, hydrogen has a mass number of 1 (one proton,no neutrons), an atomic number of 1, and an atomic weight of 1.008; helium, with two protons and two neutrons, has a mass number of 4, an atomic number of 2, and an atomic weight of 4.0026. Carbon has a mass number of 12, an atomic number of 6, and an atomic weight of 12.01115 (an average including all isotopic forms); the mass of the 12 isotope is the international standard for calculation of atomic weights.
  
  It is the nearest whole number to an atom's weight. For instance, the mass number of uranium-235 is 235.

  Terme :

  1. mass number