The amount of particles in a substance is called the number of moles.

Here's why:

* Atoms and Molecules: Everything is made of tiny particles called atoms. Sometimes, atoms bond together to form molecules.

* Mole: A mole is a unit of measurement that represents a specific number of particles. It's like a "dozen" but for atoms or molecules. One mole contains 6.022 x 10^23 particles (this is called Avogadro's number).

* Molar Mass: Each element or compound has a specific molar mass, which tells you how many grams are in one mole of that substance.

Here's an example:

* Water (H2O): The molar mass of water is 18.015 g/mol. This means one mole of water weighs 18.015 grams and contains 6.022 x 10^23 water molecules.

So, to determine the number of particles in a substance, you need to know:

1. The mass of the substance.

2. The molar mass of the substance.

Then you can use the following formula:

Number of moles = Mass of substance / Molar mass of substance

To find the number of particles:

Number of particles = Number of moles x Avogadro's number