# How should I study about moles and how they relate to things like Avogadro's number and molar mass?

##### 1 Answer

**Warning! Long answer**, but here is my revisionist view of chemical history.

#### Explanation:

Since the early days of chemistry, chemists could figure out the **relative** masses of atoms.

For example, they knew that a

For argument's sake, let's assume that they could put a "pile" of atoms on a balance and determine their total mass.

Then, if they measured out say, 1 g of hydrogen, 12 g of carbon, and 16 g of oxygen, they knew they had the same number of atoms in each pile, even if they didn’t know how many atoms or their individual masses.

They decided to use **mole**, after the Latin word for a pile of rocks.

Even today in England, which was occupied by the Romans, a pile of stones used as a breakwater is called a "mole".

It was natural to assign to each atom an atomic mass that had the same number as the mass of its mole.

Thus, the atomic masses became 1 unit for

Eventually, chemists figured out how many atoms there are in a mole of atoms, and they called it **Avogadro's Number** (

Then, if one mole of

Today, we use carbon-12 atoms as our standard, and we define a **mole** (symbol **mol**) of carbon-12 as **exactly** 12 g of carbon-12.

We say that the **molar mass** of carbon-12 is exactly 12 g.

Since it contains Avogadro's number of atoms,

**A mole of anything (atoms, molecules, ions, people, etc.) is Avogadro's number of those things**.

The mass of an atom of carbon-12 is defined as exactly 12 **unified atomic mass units** (symbol **u**).

Thus the atomic mass of a carbon-12 atom is exactly 12 u (**not** amu).

**Summary**: The mole is a convenient way to measure a desired number of atoms or molecules.