Who is the most popular chemist? Avogadro. Everyone knows his number. Okay it is a corny joke, and it is also probably a bit baffling if you have never heard of Avogadro’s number. It is one of those things that sounds a bit dry if you describe it in purely technical terms, but which is actually a stunning achievement of our species. It is simply the number of atoms in a gram of the smallest atom, i.e., hydrogen. We know the relative sizes of all the atoms. For example carbon is 12 times bigger than hydrogen. So 12g of carbon contains the same number of atoms as 1g of hydrogen. Chemists can therefore use Avogadro’s number to work out the number of atoms in any quantity of anything.
Neat as that is, the really stunning thing is that Avogadro’s number is so big. It is 602,200,000,000,000,000,000,000. Or six hundred and two thousand two hundred billion billion. In scientific notation that comes out as 6 x 10 to the power of 23, which is why the 23rd day of the 10th month has been unofficially designated by chemists as Mole Day.
The sheer size of Avogadro’s number tells us something very important about atoms. They are very small, and there are lots of them. This has all sorts of implications. For a start, being so small they can move incredibly quickly. When the Fukushima nuclear power plant blew up in 2011 it was only a few days later that atoms from it were detected in Oxford. An atom can get half way around the world nearly as quickly as a jet plane.
Atoms do have at least one thing in common with the furry version of moles. Being very small, very numerous and very mobile means they get everywhere. It has been calculated that every breath you take contains at least one atom of oxygen that was breathed by Julius Caesar.
This means that the world we live in is very closely connected and we are all near neighbours. We share an environment and we really have to live together. Issues like nuclear power and pollution affect the whole world literally. When the greens say act local think global they are onto something.
It is also bad news for chemophobes. If somebody somewhere is using something you don’t like the chances are that a few atoms of it are going to be coming your way soon. But the good news for chemophobes is that atoms are really small and couple of them, even the nastiest, isn’t going to do you any harm.
So happy Mole Day to my fellow chemists, and the non-chemists are welcome to join the celebrations too.