VanCleave's Science Fun

Your Guide to Science Projects, Fun Experiments, and Science Research

Home » How Many Atoms in A Mole?

How Many Atoms in A Mole?

By

A chemical mole is not an animal. 
A drawing of a mole is shown to clarify that in chemistry a mole is not an animal.

A chemical mole is a unit of measuring the amount of chemical substances. For the problem shown, use this mole conversion factor:

1 mole = 6.o2 x 10 23 atoms

The number 6.o2 x 10 23 is called Avagadro’s Number 

Calculate:  4.2 x 10 26 atoms of lithium (Li) are equal to how many moles of lithium (Li)? 

Dimensional Analysis steps for changing atoms to moles.
Following are step-by-step instructions for working through this problem. Please contact me if you have any questions.
 
Think: Draw a T chart to organize your numbers and units. Numbers and units above the horizontal line will be in the numerator and numbers and units below the horizontal line will be in the denominator. The vertical line represents a multiplication operation.
 
Think: Write the number and unit of the amount of the starting material. Read the problem again. It is a simple conversion problem with only one measure, which is 4.2 x 10 26 atoms of Lithium, Li. 
While is seems not necessary, write the number, unit and what is being measured–Li.
 
Think: Look at your T chart. Notice that atoms of Li is in the numerator (above the horizontal line). The only way to remove this unit is to divide by atoms of Li. So write atoms of Li in the denominator (below the horizontal line).
 
Think: The problem is to calculate the number of moles that are equal to 4.2 x 10 26 atoms of Lithium, Li.

Is there a conversion factor comparing the unit of moles to atoms? YES!
1 mole = 6.o2 x 10 23 atoms

Add the number 6.o2 x 10 23 with the atoms of Li in the denominator. 

Add 1 mole in the numerator.

Draw a line through atoms as shown. You now only have the unit of mole left in this problem. Thus when the math calculations are completed, the unit for the number answer is mole.

Think: Before you start your calculations, decide how many significant figures your answer will be in. Remember, that conversion factors are never used in determining significant figures. Thus, the significant figures of 4.2 is the number of significant figures for the answer. The answer should be in two significant figures. FYI the scientific notation does not decide significant figures.

For more information about moles, see What is a mole?

Janice VanCleave's Chemistry for Every Kid Book is a basic science experiment book, designed to help kids to learn, and adults to teach the fun of learning chemistry concepts.

Chemistry for Every Kid

Each of the 101 chemistry experiments has a purpose, list of materials, step-by-step instructions and illustrations, expected results, and a science explanation in understandable terms.