Counting Particles: the Mole

Particles are far too small to count one by one, so chemists count them in packs, like eggs in dozens. The pack is the mole (mol): $6.02 \times 10^{23}$ particles.

One mole of water molecules: about 18 mL

A mole counts anything: atoms, molecules or ions. Say which one: 1 mol of water molecules, 1 mol of iron atoms.

The number in one mole is written N_A. The number of particles in $n$ moles is

$$N = n \times N_A$$