Short Notes #5

Avogadro’s Number

The Avogadro Number is the proportionality factor that relates the number of constituent particles (molecules, atoms or ions) contained in one mole of a substance. Its SI unit is the reciprocal mole, and is exactly 6.02×10²³ mol⁻¹.

Robert Millikan, an American Physicist, was the first to measure the charge on an electron which helped determine the Avogadro’s Number. The electron charge is measured as 1.6021765 x 10^-19 coulombs per electron. The Faraday is the charge on a mole of electrons and is estimated as 96,485.34 coulombs per mole of electron. The Avogadro’s Number is then obtained by dividing the charge on a mole of electrons by the charge on a single electron i.e.,

Avogadro’s Number = (charge on a mole of electrons / charge on a single electron)

                                  = (96,485.34) / 1.6021765 x 10^-19)

                                  = 6.02 x 10²³ particles per mole