You often measure the amount of something by one of three different methods - by count, by mass, and by volume. Most often objects are large enought to count out indivudually. In the case of chemical particles, the particles are so small count each particle individually would be very time consuming and tedious. Chemist developed a unit called the mole to specify a specific number of particles. In one mole of a substance there are 6.022x10^23 particles!