The Mole
The Mole
Sometimes it is important to know exactly how many particles (e.g. atoms or molecules) are in a sample of a substance, or what quantity of a substance is needed for a chemical reaction to take place.
The amount of substance is so important in chemistry that it is given its own name, which is the mole.
Definition: Mole
The mole (abbreviation “mol”) is the SI (Standard International) unit for “amount of substance”.
The mole is a counting unit just like hours or days. We can easily count one second or one minute or one hour. If we want bigger units of time, we refer to days, months and years. Even longer time periods are centuries and millennia. The mole is even bigger than these numbers. The mole is \(\text{602 204 500 000 000 000 000 000}\) or \(\text{6.022} \times \text{10}^{\text{23}}\) particles. This is a very big number! We call this number Avogadro's number.
Definition: Avogadro's number
The number of particles in a mole, equal to \(\text{6.022} \times \text{10}^{\text{23}}\).
If we had this number of cold drink cans, then we could cover the surface of the earth to a depth of over \(\text{300}\) \(\text{km}\)! If you could count atoms at a rate of 10 million per second, then it would take you 2 billion years to count the atoms in one mole!
Did You Know?
The original hypothesis that was proposed by Amadeo Avogadro was that “equal volumes of gases, at the same temperature and pressure, contain the same number of molecules”. His ideas were not accepted by the scientific community and it was only four years after his death, that his original hypothesis was accepted and that it became known as “Avogadro's Law”. In honour of his contribution to science, the number of particles in one mole was named Avogadro's number.
We use Avogadro's number and the mole in chemistry to help us quantify what happens in chemical reaction. The mole is a very special number. If we measure \(\text{12.0}\) \(\text{g}\) of carbon we have one mole or \(\text{6.022} \times \text{10}^{\text{23}}\) carbon atoms. \(\text{63.5}\) \(\text{g}\) of copper is one mole of copper or \(\text{6.022} \times \text{10}^{\text{23}}\) copper atoms. In fact, if we measure the relative atomic mass of any element on the periodic table, we have one mole of that element.
This lesson is part of:
Quantitative Aspects of Chemical Change