Knowledge database: Stoichiometry: Particle number

The particle number is a physical quantity without an unit, which expresses the number of particles (atoms, ions, molecules or other). It is indicated by the letter N, and usually, in the parentheses beside the letter N, the particle type is mentioned.

If one knows the mass of a particle, and the mass of all the particles that one has, the number of particles can easily be calculated by dividing the mass of all particles by the mass of one particle. These particles, of course, can be atoms, molecules, subatomic particles, ions, or any other type.

One of the most important values of the particle number as a physical quantity, is the Avogadro's number (N_A), which is actually the number of particles in one mole of any substance.