1. Learning Objectives: To understand the concept of a mole

2. Atoms are incredibly small. We cannot measure the mass of an individual atom, it is just too small. We know that different atoms have different masses. We need a way of telling how heavy different atoms are compared to each other.

3. We measure the masses of atoms relative to one another. We need to work out what one mass unit is so that we can then say what other masses are. We use 12 C as our standard and measure other masses relative to this.

4. A mole is just a number. One mole is the number of particles that is the same as the number of atoms in 12g of 12 C. The number is huge: 602200000000000000000000 (ish) We write it as 6.022 x 10 23.

5. Examples 1 mole of sodium contains 6.022 x 10 23 sodium atoms. 1 mole of argon contains 6.022 x 10 23 argon atoms. 1 mole of oxygen molecules contains 6.022 x 10 23 oxygen molecules. 1 mole of carbon dioxide molecules contains 6.022 x 10 23 carbon dioxide molecules.