Did the idea of a mole ever confuse you in school? The definition doesn’t help - “..amount of a substance that contains the same number of elemental particles as 12 gms of Carbon-12”
It took me a while to understand that a mole was just a number, no dimensions. And a little while later, I realised the wonderful, mind blowing idea behind it. It was so comprehensively buried! Because, when you think about it, what the idea of a ‘mole’ is saying is that the weight of atoms comes from protons and neutrons.
No matter how different Uranium is from Oxygen, the weight of each comes from the same subatomic particles. What an insight! Especially at a time when people believed that the atom was indivisible.