What exactly is a mole?
The definition of what a mole is changed the world of chemistry. Moles allow us to move from a level of molecules to more manageable units through the weight, or what is the same, any chemical can know how many atoms and molecules a sample contains by simply weighing it. How?
Basically a mol of any substance is a weight equal to the molecular weight expressed in units of atomic mass. This implies that a mole of any substance contains exactly the same number of molecules.
All elements of the periodic table have a certain atomic mass. For example, hydrogen has an atomic mass of 1.0079, while oxygen has an atomic mass of 15.999. Thus a water molecule (H2O, two hydrogen atoms attached to one oxygen) will have an atomic mass of approximately 18. Or what is the same, a mole of water will weigh approximately 18 grams. Likewise a mole of neon atoms will weigh 20,180 grams. But how can you tell how many molecules exist in these 18 grams of pure water, that is, in a mole of water?
Amadeo Avogadro discovered in the early nineteenth century the relationship between the quantity of molecules or atoms of a substance and the moles. In general, a mole of any substance contains 6,022 x 1023 molecules or atoms of the substance. So In a mol of water (H2O) there are 6,022 1023 molecules of H2O, or what is the same, 2 6,022 1023 atoms of hydrogen and 6,022 1023 atoms of oxygen.
Mole Day is celebrated every year on October 23 in the United States between 6:02 in the morning and 6:02 in the afternoon taking advantage of the digits of the Avogadro number.
Unit of measurement
A mole is simply a unit of measurement. Units are invented when existing units are inadequate. Chemical reactions often take place at levels where using grams would not make sense, but using absolute numbers of atoms / molecules / ions would also be confusing.
Like all units, a mole must be based on something reproducible. For example, a mole is the amount of anything that has the same amount of particles found in 12,000 grams of carbon-12. That number of particles is the number of Avogadro, which is approximately 6.02x1023. A mole of carbon atoms is 6.02x1023 carbon atoms. Basically, that’s why this particular unit was invented.
Why not simply limit ourselves to units such as grams (and nanograms and kilograms, etc.)? The answer is that moles give us a consistent method to convert between atoms / molecules and grams. It is simply a convenient unit to use when performing calculations. It may not be very convenient if we are learning how to use it for the first time, but once we become familiar with moles, it will be as normal as when we use a dozen or a byte.
