[lemonoman]

This may or may not be question-of-the-day worthy, but I certainly found it interesting.

"Why do we use the term 'mole' to describe Avogadro's number of atoms?"

I'll let people chew on this I guess, while I go on about something else.

Wikipedia's article on Avogadro's number says that The value of Avogadro's number depends on the definition of the mole, which depends on the definition of the kilogram. Both definitions, especially that of the kilogram, are arbitrary: the kilogram system is currently based on the mass of a particular "standard" bar of metal in France.  I remember reading somewhere that because that particular matel bar is cleaned every so often, and thus the standard for one kilogram actually decreases ever-so-slightly with each cleaning.  I suppose that changes  Avogadro's number, too?

Ever time is based on the wavelength from a certain type of laser (which is fundamental).  Maybe a kilogram should be standardized to a fundamental constant as well (EXACTLY 6.022 × 10^{23 12}C atoms)?  Maybe this is too hard to measure?

[Borek]

Not time, but length is defined with the use of wavelength.

As for kg definition - physics are working on the problem, but it is much tougher then you think. Best idea is to define an object that is easily reproducible and has a 1kg mass. However, reproducibilty of the physical objects is hard to obtain. While it doesn't matter for normal circumstances, irregularities in crystalic structure of any object add to its internal energy, and energy is a mass. Thus two identical objects are not necesarilly identical, and we are going back to the place where there is only one standard object.

I remember reading some articles on the subject, probably some materials can be Googled.

[lemonoman]

My mistake, I should have been more careful :

WikiPedia tells me that "The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom." - this isn't 'light' as I had thought, but a splitting from interacting magnetic fields...

[bigbluezuk]

You mean the actual term "mole?" or why its 6.02e23?  The mole is how many carbon atoms are in 12.000 (how many significant figures we can measure mass to)g of 99.99(however pure we can get it)%.  I think we are out to 9 sigfigs in Avogadro's number so far.  Why the term mole?  Id like to know that myself.

=D

[mike]

I always thought the term mole came from the term molecule or molecular weight (gram molecular weight etc). Anyone else actually know?

[AWK]

http://www.etymonline.com/index.php?term=mole

[mike]

Great so it is a short form of the word molecule. Cool

[Custos]

Mass is the only one of the seven basic measurement standards that is still defined in terms of a physical artifact -- a century-old platinum-iridium cylinder weighing one kilogram that is housed in a special vault in France.

Under the auspices of the International Bureau of Weights and Measures (BIPM), near Paris, the decision has been made that international effort will focus on two ways of re-defining the kilogram: one of which involves making a perfect sphere from a single crystal of exceptionally pure silicon.

The work will be done with the close cooperation of Australia’s National Measurement Institute (NMI) and CSIRO’s Australian Centre for Precision Optics (ACPO), which share the same site in the Sydney suburb of Lindfield.

While a physical object will still be necessary for calibrating scales and balances, the silicon atoms in the sphere will always remain the same. It is for this reason that the scientists working on what’s known as the Avogadro Project are collaborating to determine what is effectively the number of atoms in a sphere. Once the number of atoms is known, the definition of the kilogram can be based on it from then on.
 
Dr Barry Inglis, Chief Executive of NMI says.The best sphere the ACPO team has made had a total out-of-roundness of 35 nanometres. That is, the diameter varies by an average of only 35 millionths of a millimetre, making it probably the roundest object in the world.

See: http://www.csiro.au/news/PerfectKilogramMediaRelease.html