Today’s factismal: There are about as many atoms in 5 1/2 ounces of oxygen as there are stars in the universe.
If you had been a chemist in the 1800s, you would have had a real problem. You knew for a fact that oxygen plus carbon would make water(H2O), but you would be able to say how much oxygen or how much hydrogen was needed to leave nothing but water in the reaction chamber. Sometimes you’d have oxygen left over and sometimes you’d have carbon left over and you’d always have a big mess. It was uncertainties like this that kept chemistry from being an exact science.
The reason that chemistry was an uncertain science was because the number of oxygen atoms in a pound of oxygen is different than the number of hydrogen atoms in a pound of hydrogen. (This is why Mark Whatney blew up the lab in The Martian.) Because chemistry takes place on the atomic scale, you couldn’t just add two pounds of hydrogen to one pound of oxygen and get nothing but water; you had to find some way of scaling the weight (or, more appropriately, the masses) of each chemical so that you’d be adding the right number of atoms. Fortunately, a scientist by the name of Avogardo pointed the way.
Avogardo (or “Avocado” as he is known to all freshman chemistry students) had the bright idea in 1811 that the volume of space taken up by a gas at a given pressure and temperature might be related to the number of atoms in that gas; based on that, he and other scientists were able to derive the relative atomic weights of the elements. It took the chemists nearly a century, but by 1909, we had a periodic table that listed the atomic weight of each element. That allowed us to know exactly how much of each to add in order to get reactions that worked perfectly every time.
Avogardo and the chemists who came after him called the standard amount of stuff a mole (short for “molecular volume”). And, because it was Avogardo’s bright idea that made it all possible, the number of atoms (or molecules) in a mole is known as Avogardo’s number. And it is a mighty large number – there are 6.02 x 10^23 atoms of oxygen in 16 grams (one mole) of oxygen. To give you an idea of how many atoms that is, just go outside tonight and take a look at the night sky. If you were to count every star in every galaxy in the universe, there would be about 10^24 stars. So there are as many atoms of oxygen in ten moles of oxygen as there are stars in the mole of the universe!
In honor of Avogardo’s discovery, today is Mole Day (because it is 10/23 – get it?). So take part in a mole day celebration somewhere. Go eat a mole cake and drink some mole juice. And then make a un-moley mess, just so you can appreciate why chemists were so happy to become an exact science!