amount of substance & chemical entities

G2. RELATIONSHIP BETWEEN AMOUNT OF SUBSTANCE & NUMBER OF ENTITIES

Very, very large or very, very small quantities are often difficult for us to visualize and so therefore appreciate their physical significance.

Atoms of elements have masses of the order of

-24

and radii in the region of

-10

m, far, far too

small to be able to handle individually in almost all but the most highly specialized research laboratories.

When it comes to assessing atoms in bulk, a convenient unit needs to provide for a large enough quantity of material to be handled, ideally on the gram or kilogram scale of mass. A very great number of atoms

(»10

) happens to be in the unit that provides such convenience.

The large unit adopted for atoms called the MOLE is effectively a chemical measure. It provides the link between the numbers of atoms on the nano-scopic scale and meaningful amounts of material which can be handled on the macroscopic (bulk) scale, corresponding to masses from milligrams and upwards.

It is an 1897 translation of the German unit Mol - a contraction of the German word Molekül (molecule).
While the introduction of this term in the 1890s is usually attributed to Wilhelm Ostwald (1853-1932), it is equally likely that his student, Walther Nernst (1864-1941), was the first coin it.