# What is the difference between molar mass and atomic mass?

Aug 9, 2017

Molar mass is the mass of one mole of a substance.

Atomic mass is the mass of one individual unit of a substance.

An important concept regarding the mole is that
the atomic mass in $\text{amu}$ of a substance is numerically equivalent to the mass in $\text{g}$ of one mole of that substance.

To illustrate this fact, let's look at the compound sodium chloride ($\text{NaCl}$).

The atomic mass of $\text{NaCl}$ can be found by using the atomic masses of the individual elements found on a periodic table:

overbrace(22.99color(white)(l)"amu")^"sodium" + overbrace(35.45color(white)(l)"amu")^"chlorine" = overbrace(color(red)(ul(58.44color(white)(l)"amu")))^"sodium chloride" $\leftarrow \text{ atomic mass}$

This is numerically equivalent to the molar mass of $\text{NaCl}$. That is to say,

overbrace(22.99color(white)(l)"g/mol")^"sodium" + overbrace(35.45color(white)(l)"g/mol")^"chlorine" = overbrace(color(red)(ul(58.44color(white)(l)"g/mol")))^"sodium chloride" $\leftarrow \text{ molar mass}$

So, the mass of one unit of $\text{NaCl}$ is $58.44$ $\text{amu}$, and the mass of one mole of $\text{NaCl}$ is $58.44$ $\text{grams}$.