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Polymer Chemistry and Biomaterials Group
Polymer Chemistry and Biomaterials Group

People tend to like holidays, so Your Formula should love ‘scientific’ holidays. Today, October 23th, at 6:02 a.m. the Chemical Holiday started. Which holiday you ask? Well you may get a hint if we write today’s date in US style (i.e. 6:02 a.m. 10/23). Doesn’t that look awfully familiar? Indeed, it’s Avogadro’s Number (6.02*1023)…

So today we celebrate ‘Mole Day’!

We are of course speaking about the amount of substance rather than the furry dirt dwellers or the dark spots on our skin.

One mole is the amount of any substance that contains as many elementary entities (e.g. atoms, molecules, ions or electrons) as there are atoms in 12 grams of pure carbon-12 (12C), the isotope of carbon with relative atomic mass 12 (source Wikipedia).

To put it more simply, a mole is like a dozen, but instead of containing just 12 particles like the dozen, the number  of atoms or molecules in a mole is much greater. Since atoms and molecules can be as tiny as 0.1 nm (or about 100.000 times smaller than the width of human hair), it is quite obvious we can’t simply put atoms in a box and count them individually.

Bankers may count money in terms of millions (106), chemists count their atoms or molecules in the somewhat more crude amount of ‘6.02*1023 particles’.

This may seem like an awful lot of particles, but in fact 1 gram of graphite, the material that makes up the core of your pencils, contains 5.02*1022 carbon atoms. If you’re gasping for air on reading this figure,  don’t even think about the number  of molecules that make up the atmosphere you are breathing!


Since the mole is so closely related to all aspects of chemistry, Maurice Oehler, an American high school teacher, proclaimed October 23th to be ‘Mole Day’. On this day schools organise chemistry related activities to get their students more interested in sciences, especially chemistry. Although Mole Day is mainly celebrated in the US and Canada, we are optimistic that European teachers will embrace this Holiday as well and use it to make their students more aware of the importance of chemistry.



Happy Mole Day!

Contribution by Geert-Jan Graulus (PBM)