Number of carbon atoms in 12 g of the carbon-12 isotope (6.022045 × 1023). It is named after Italian chemist Amedeo Avogadro. The relative atomic mass of any element, expressed in grams, contains this number of atoms and is called a mole. For example, one mole of any substance contains 6.022 × 1023 particles. One mole of carbon has a mass of 12 g.