Until , when Bonse and Hart demonstrated the first X-ray interferometer 3 , the value of N A was used for determining the lattice spacings in crystals from their volumes and masses. Now, X-ray interferometry enables counting how many silicon atoms are aligned in a crystal, the length of which is measured by optical interferometry, relating atomic dimensions to the wavelength of visible light 4.
Using this method, the number of atoms in a 1 kg sphere of high-purity 28 Si an artist's impression is pictured, featuring Avogadro and his law was counted and N A determined by dividing the molar volume by the atomic volume of 28 Si measured via X-ray interferometry. The current most accurately measured value of N A , 6. High-precision measurements of the Avogadro constant are important for being able to quantitatively connect the macro- and microscales — obviously, knowing N A , one can switch between molar mass and particle mass.
But in addition, metrologists are planning to define the kilogram and the mole via the Planck and Avogadro constants 6. Before that can happen, an accurate determination of N A needs to be realized. By fixing N A , the atomic model of matter becomes embedded in the International System of Units SI and the mole redefined in terms of the number of entities it represents.
Furthermore, as the ratio between the 28 Si mass and the Planck constant can be accurately measured using atom interferometry, and as we are now able to 'count atoms', macroscopic prototypes with an exactly known amount of substance and mass can be realized neglecting Einstein's mass—energy equivalence principle and atoms therefore having unique and well-defined masses. Magnenus, J.
Google Scholar. Mana, G. Rivista del Nuovo Cimento 18 , 1—23 Article Google Scholar. Bonse, U. Massa, E. Data 44 , Azuma, Y. Metrologia 52 , — Fischer, J. Nature Phys. Download references. They'd use "yotta" in the same way they use "mole", not doing calculations with the actual number it represents and not being at risk of other types of error.
Here's a similar question but it's mixed in with the idea of measuring number rather than mass or volume - Why do people still use the mole unit in chemistry? This other similar question mainly addresses the uncommonness of quantities as big as 1 mole in other areas of life - The mole is used extensively in chemistry, why not elsewhere?
The thing about large numbers is that they are large. Almost everybody who grew up in a metric country can name at least three SI-prefixes: kilo, centi and milli. I often work with milli- or micromoles of substances in my research.
With the mole, everything one uses in the lab will nicely fall into something between nano and kilo. It also helps to have a single unit there. Molar mass is expressed in grams per mole, concentrations in moles per litre and many more. If there were no unit, it would be simple grams per 1 or 1 per litre — precisely the reason why some people prefer to use rad or some other way to show radians rather than just writing the number.
If there was no name for this unit, it would have to be invented. The good thing about the size definition of the mole is, as noted above, that it brings everything into one general range. Thankfully, those are the ones that are most used in everyday life, too excluding nano and maybe micro. Same meaning, different exactness. If the moles are soon defined by mere counting rather than weighing atoms then so be it. Nothing will change for me in practice. All of those constants have to stay the same for many of the formulations of Chemistry to be correct, so we would have stumbled across this magic number one way or another.
While it might be true and I don't know this that the mole was not defined with any of that in mind, it's really quite convenient if you ask me to have a mole be both a unit and a physical constant which everyone knows.
After all, every knows Avogadro's number and the ideal gas constant. The thing about the mole is that it simplifies chemistry terminology in a way that can't be avoided if you want to talk about chemical reactions.
A mole is a count of the things involved in a reaction, not necessarily a count of the atoms involved. So a mole of oxygen gas contains two moles of oxygen atoms. A mole of a protein contains hundreds of moles of amino acid resides and, well, an awful lot of moles of atoms. When thinking about this we don't usually have to worry about the number of units of the thing we are discussing. If we didn't have the idea of the mole, we would have have to use much longer descriptions every time we talked about chemical entities or chemical reactions to be clear what it was we were actually counting.
A mole of carbon atoms would have be described as Zetta carbon atoms: a mole of carbon is shorter. Everything would have its own name. And we'd have to use a lot of exa and zetta SI prefixes which could get awkward in calculations. The value of the mole doesn't matter that much most of the time when thinking about reactions: only the ratio.
That it is an very large number is mostly unimportant and the calculations chemists mostly do use molar ratios where they only need to calculate using atomic or molecular mass for the components in the reaction. Including the actual size of the mole in these calculations would introduce very large and unnecessary numbers that would end up cancelling out in the small number of calculations where nobody made an error and would give completely incorrect answers in all the others where people got confused by all the extra prefixes or digits.
Tha actual size of the mole is a little arbitrary, but has the advantage it is the sort of scale chemistry is often done on. You can do a reaction with that scale on your tabletop. And you don't need to count or even remember Avogadro's constant to do it or any of the calculations associated with it. I could happily talk about fully electrolysing a mole of water to produce a mole of hydrogen and half a mole of oxygen with no mention of Avogadro, no big-number SI units.
PS The mole is truly inconveniently large for some objects not on the atomic scale. A mole of moles the furry burrowing mammal would make up a sphere about the same size as the moon. Moles are simply a built in conversion factor that keeps us from either having to use amus as our macroscopic unit of mass, or grams or kgs as our microscopic unit of mass.
You can derive a meter, joule, Newton, second or K from a gram of water in the Earth's gravitational field. Moles are not a fundamental concept in chemistry, they are a practical concept, but the ability to move between non-conforming unit bases is fundamental as long as we live in a universe where not every scale of matter is a precise power of ten up from the last one. We either use the fundamental quantum unit of mass in chemistry when describing molecules and dispense with our units of force, energy, power, pressure, volume, and length, or we ignore the chemical quantum of mass, or we find a way to move from one to another.
I am familiar with all the SI prefixes, but even if I was not familiar, I would prefer to learn a pair of universal prefixes rather than deal with the mole and all the issues, inconsistencies, and headaches it brings to us:. Part 1: the case of chemistry. Gary Price.
Accred Qual Assur — Old Concepts and New. To do this we need to know the mass of an individual atom or the mass of a specific number of atoms. The mass of one carbon atom is very tiny - 1. This mass is a bit cumbersome to deal with so a unit of mass was invented to make it easier to discuss the mass of atoms and molecules - the atomic mass unit amu.
It was defined such that the carbon atom was exactly equal to If an atom weighed twice as much as a carbon atom it had a mass of The answer is 6. Because Every atomic mass on the periodic table has the unit amu , and if we have enough of an element measured out in grams to equal its atomic mass then we have 1.
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