# Question dca94

A mole of a substance represents a collection of atoms or molecules; in order to have 1 mole of any substance you need $6.022 \cdot {10}^{23}$ atoms (or molecules) of that substance.
So, if you have 1 billion atoms, that is equivalent of ${10}^{9}$ atoms. To find out how many moles of that substance you have, just set up a conversion factor
${10}^{9}$ "atoms" * ("1 mole")/(6.022 * 10^23"atoms") = 1.66 * 10^(-15)# $\text{moles}$