The Mole is a very powerful concept.
Simply put, the mole represents a number. Just as the term dozen refers to the number twelve, the mole represents the number 6.02 x 10^23.
Now that’s a big number! While a dozen eggs will make a nice omelet, a mole of eggs will fill all of the oceans on earth more than 30 million times over. Think about it: It would take 10 billion chickens laying 10 eggs per day more than 10 billion years to lay a mole of eggs. So why would we ever use such a big number? Certainly the local donut store is not going to “supersize” your dozen by giving you a mole of jelly-filled treats. The mole is used when we’re talking about numbers of atoms andmolecules. Atoms and molecules are very tiny things. A drop of water the size of the period at the end of this sentence would contain 10 trillion water molecules. Instead of talking about trillions and quadrillions of molecules (and more), it’s much simpler to use the mole.
Why is this number of atoms (6.02 x 10^23) so special, and what makes the mole so powerful?
The reason is that precisely for a mol or 6.02 x 10^23 of any atom or molecules, its atomic mass or relative molecular mass = its mass in grams!
Below, we can see the atomic mass of Hydrogen (1.00… because it has 1 proton) and Oxygen (15.999 because it has 8 protons & 8 neutrons)…
And then look!
1 mol or 6.02 x 10^23 hydrogen atoms have a mass on of 1 gram!!!
And hey, so does Oxygen too, because 1 mol of oxygen atoms have a mass of nearly 16g!
How did Scientists discover this idea?
It turns out that a very clever man named Avogadro had a concept that “equal volumes of all gases at the same temperature and pressure contain the same number of molecules”
After scientists have discovered the mass of a proton and mass of a neutron, they can easily do the calculation to find out how many atoms/molecules are there in say 1 litre of oxygen.
And that they settled on the mole as a unit is not a coincidence! It makes it so inter-convertable with grams and kilograms and volume!
For a very good explanation on how the mol concept came about, please visit this link!
Heres a reward for reading all the way to the end!