The mole is the standard method in
chemistry for communicating how much of a substance is present. A mole is basically
an amount of stuff.

Here is how the International
Union of Pure and Applied Chemistry (IUPAC) defines "mole": The mole is
the amount of substance of a system which contains as many elementary entities
as there are atoms in 0.012 kilogram of carbon-12. When the mole is used, the
elementary entities must be specified and may be atoms, molecules, ions, electrons,
other particles, or specified groups of such particles.

One mole contains as many entities as there are in 12 grams of carbon-12 (or 0.012 kilogram). There are 6.022 x 1023 atoms in 12 grams of carbon-12. Therefore explained in simpler terms 'One mole of any specified entity contains 6.022*1023 of that entity':

__One mole of bricks
contains 6.022*1023 bricks
One mole of peas contains 6.022*1023 peas
One mole of water contains 6.022*1023 of water molecules.__

6.022*1023 is called Avogadro's Number after the Italian chemist Amedeo Avogadro. However, counting atoms or molecules is very difficult since they are so small. However, we can "count" atoms or molecules by weighing large amounts of them on a balance.

When we weigh one mole of a substance on a balance, this is called a "molar mass" and has the units g/mol (grams per mole). This idea is very critical because it is used all the time.

__A molar mass is
the weight in grams of one mole.__

__Therefore, a molar mass is the mass in grams of 6.022 x 1023 entities.__

__The molar mass of a substance is the molecular weight in grams. __