Avogadros Number (Chemistry Glossary Definition)

Avogadros number, or Avogadros constant, is the number of particles found in one mole of a substance. It is the number of atoms in exactly 12 grams of carbon-12. This experimentally determined value is approximately 6.0221 x 1023 particles per mole. Avogadros number may be designated using the symbol L or NA. Note that Avogadros number, on its own, is a dimensionless quantity. In chemistry and physics, Avogadros number usually refers to a quantity of atoms, molecules, or ions, but it can be applied to any particle. For example, 6.02 x 1023 elephants is the number of elephants in one mole of them! Atoms, molecules, and ions are much less massive than elephants, so there needed to be a large number to refer to a uniform quantity of them so that they could be compared relative to each other in chemical equations and reactions. History of Avogadros Number Avogadros number is named in honor of the Italian scientist Amedeo Avogadro. Although Avogadro proposed that the volume of a gas at a fixed temperature and pressure was proportional to the number of particles it contained, he did not propose the constant. In 1909, French physicist Jean Perrin proposed Avogadros number. He won the 1926 Nobel Prize in physics for using several methods to determine the value of the constant. However, Perrins value was based on the number of atoms in 1 gram-molecule of atomic hydrogen. Later, the constant was redefined based on 12 grams of carbon-12. In German literature, the number is also called the Loschmidt constant.