MadSci Network: Chemistry
Query:

Re: What is origin of 'Mole'

Date: Sat Mar 7 15:50:07 1998
Posted By: Sue Klemmer, Secondary School Teacher science
Area of science: Chemistry
ID: 888901189.Ch
Message:

Dear Marie Farwell:

I have not been able to find out the complete origin of the etymology of "mole", but I do have some information for you on the history of the concept.

The nineteenth century was a time of much discovery and controversy over the nature of matter: was it particulate or continuous? Many different words were used among those who believed that matter was in the form of discrete bits, such as atom, particle, corpuscle, and molecule. From the small amount of reading I have done "molecule" seems to be a French term that shows up in the work of chemists such as Gay-Lussac and Avogadro. In 1811 Avogadro proposed his famous Hypothesis: equal volumes of gas, at the same temperature and pressure, contain equal numbers of molecules. He had no way to actually count the number of molecules present, but the concept of the number of molecules present in a unit volume of gas at standard conditions was established and used throughout the 1800's. It shows up clearly in the Ideal Gas Law (PV = nRT), where n represents the number of gas molecules. I suspect that the term "mole" originated in France in the late 1800s. I do know that mole came from "molecule", which as I said before I believe is a French word. And the mole is listed as a metric unit, and the French did originate the metric system. The McGraw-Hill Encyclopedia of Science states that "mole" only became widely used around 1900.

What about the actual size of the mole? As you undoubtedly know, a mole is 6.02 x 10^23 items, an amazingly large number (a mole of pennies distributed evenly among Earth's population would give every man, woman, and child one trillion dollars). Essentially, the mole represents a conversion between grams and atomic mass units. During the 1800s, a system of relative masses or weights of molecules was being developed. Although it was not possible to determine how many particles were contained in that standard sample of gas, it was possible to determine the relative masses of equal numbers of molecules. For example, oxygen was eventually found to be 16 times heavier than hydrogen, and sulfur to be about twice as heavy as oxygen. A standard was needed in order to create a scale of atomic weights, and the original one set oxygen at 16 grams. This means that the standard number of particles (one mole) are those present in 16 g of oxygen.

There were several attempts in the 1800's to use the gas laws and the new field of kinetic-molecular theory to calculate the number of particles in a standard volume of gas at 0°C and 1 atmosphere pressure. But accurate measurements required the discoveries of atomic structure at the turn of the century. Once it was possible to count the protons and neutrons in an atom, a scale of atomic weights based more or less on the mass of a proton (atomic mass units) was created. Most oxygen atoms mass about 16 amu. So, if there are 16 amu in one atom of oxygen and 16 g in one mole of oxygen, then the number of amu in one gram is equivalent to the number of atoms in one mole. Planck, Einstein, Perrin, and Millikin used various methods based on quantum and atomic theory to make a series of calculations for the value of "n" between 1900 and 1917. Today1s value is based on x-ray crystallography methods.

I hope this provides some of what you were looking for. I am glossing over a lot of history here, from the raging controversies in the 1800's over the existence of molecules to the raging controversy over the existence of isotopes in the 1900's. If you are interested, the highlights can be found in any history of chemistry (such as the classic The Atom by Isaac Asimov or the new Creations of Fire by Cobb & Goldwhite).

Yours - Sue Klemmer


Current Queue | Current Queue for Chemistry | Chemistry archives

Try the links in the MadSci Library for more information on Chemistry.



MadSci Home | Information | Search | Random Knowledge Generator | MadSci Archives | Mad Library | MAD Labs | MAD FAQs | Ask a ? | Join Us! | Help Support MadSci


MadSci Network, webadmin@www.madsci.org
© 1995-1998. All rights reserved.