Estimating the Value of Avogadro's Number Using Graphite as an Example

To estimate the value of Avogadro's Number using graphite, you should have already determined and recorded the values for the following quantities:

The variables are:

                           N = Avogadro's Number,
                           Z = number of atoms within the crystal unit cell,
                           M = average atomic mass of the atoms,
                           D = density of the substance,
               and       V = volume of the crystal unit cell.
 

Use the following formula to get a value for Avogadro's Number:

How does this value compare to the currently accepted value for Avogadro's Number?
 

Amadeo Avogadro proposed, in 1811, that equal volumes of gas contains an equal number of atoms or molecules, if the two volumes are held at the same temperature and pressure. This proposal became known as "Avogadro's Hypothesis". Even if Avogadro did not determine a numerical value for the number attributed to him, he has nevertheless planted the "seed" for it.

The first determination for the value of Avogadro's Number was made by Robert Brown (known for "Brownian" motion) in 1827.

Stanislao Cannizarro, in 1860, used Avogadro's Hypothesis as the basis for establishing a reasonable set of atomic weights for a number of elements. These atomic weights were used to obtain more accurate values for Avogadro's Number.

Robert Millikan (1923 Nobel Prize for Physics) performed his famous oil drop experiments in the 1920's. His work helped to establish a value of Avogadro's Number with improved accuracy that was cited by most chemistry textbooks into the early 1970's.

The table samples the numerical value for Avogadro's Number through the years to trace the quest for more digits and accuracy for the number. It is a miniature version of the quest for digits for the transcental number: PI.