1. Amedeo Avogadro
In order to state that equal volumes of all gases at the same temperature and pressure contain the same number of molecules, Amedeo Avogadro used the ideas of Gay-Lussac in the year 1811.

2. Avogadro's Principle
If we assume that equal volumes of all gases contain the same number of molecules, then by measuring the mass of the same volume of different gases, we can determine the relative weights of each element. It follows then that a sample of any element,weighing an amount in grams numerically equal to it’s atomic weight, contains the same number of atoms as any other element meeting the same requirement.

3. The number of atoms in any given element is known as Avogadro's number and has been determined to be equal to:
6.02 x 10^23

4. Avogadro’s Number
The atomic weight of any element that is being expressed in grams contains 6.02 x 10^23 atoms of the element.

5. The Mole The molecular weight of a substance expressed in grams.
6.02 x 10^23 H atoms= 1 mol H
and
6.02 x 10^23 Al atoms= 1 mol of Al