The Mole: counting what you can't see

One carbon atom weighs about 0.00000000000000000000002 g. No balance on Earth can weigh it, and nobody can count 10²³ of anything — not even the most patient person in your family.

The kiryana shopkeeper solved this long ago. He doesn't count rice grains — if he did, you'd still be waiting for your daal. He weighs 1 kg, and that's roughly the same number of grains every time.

Chemists do exactly the same. They weigh a fixed pack of particles. That pack is called a mole.