Moles

In chemistry a mole is a quantity of atoms, just like a ream of paper is a quantity of sheets of paper

A ream of paper is 500 sheets ofPaper.

What is a chemical mole?

A mole of atoms is 6.02 x 1023 atoms

That’s 602000000000000000000000 atoms

Why do we need moles?

Atoms and molecules are very small so they cannot be counted directly. In chemistry we usually weigh out elements and compounds.

However, simply weighing something does not tell us how much there is (i.e. how many atoms or molecules).

For example lead atoms are much bigger than hydrogen atoms, so 5g of hydrogen would contain far more atoms than 5g of lead.

6.02 X 1023  Blood Cells: Would be more than the total number of blood cells found in every human on earth.

6.02 x 1023 = a big number!

6.02 X 1023  Watermelon Seeds: Would be found inside a melon slightly larger than the moon.6.02 X 1023  Pennies: Would make at least 7 stacks that would reach the moon.

602000000000000000000000A special number

Also known as Avagadro’s number (constant)

Amedeo Avogadro

Is the number of atoms in 1 mole of a substance.

But also:

It is the number of atoms in exactly 12g of carbon

Moles are related to Relative Atomic mass

Carbon has a relative atomic mass of 12

As we weigh things in grams we say that in 12g of carbon atoms there is 1 mole of carbon atoms

The relative atomic mass of hydrogen is 1Therefore a hydrogen atom is 12 times lighter than a carbon atom.

CarbonRelative atomic mass = 12 1 mole of carbon atoms weighs 12g1

HydrogenRelative atomic mass = 11 mole of hydrogen atoms weighs 1g

Hydrogen relative atomic mass =1

1 mole = 1gwhich contains 6 x 1023 atoms

Carbon, relative atomic mass = 12

1 mole = 12gwhich contains 6 x 1023 atoms

Oxygen, relative atomic mass =

1 mole = which contains atoms

Potassium, relative atomic mass =

1 mole = which contains atoms

Arsenic, relative atomic mass =

1 mole = which contains atoms

16

16g 6 x 1023

39

39g 6 x 1023

75

75g 6 x 1023

What is the mass of:1 mole of nitrogen atoms?2 moles of oxygen atoms?0.5 moles of copper atoms?

How many moles are there in:11g of Boron atoms?3g of carbon atoms?80g of calcium atoms?

14g32g32g

1 mole0.25 moles2 moles

Useful equation!

Number of moles =Mass of element (how much you have)

Relative atomic mass of the element

For example. How many moles are there in 4 g of calcium?

Number of moles = 4

40= 0.1

MASS

MOLES

How much you have in g

The number of moles you have of the substance

FORMULA MASS

(Relative atomic mass (atoms) or relative formula mass (molecules and compounds)

Magic triangle

Moles are not just for atoms!

You can also have a mole of a molecule or a compound.

Diatomic molecules

An oxygen molecule contains 2 atoms of oxygen

The formula mass of an oxygen molecule is

1 mole of oxygen molecules weighs

1 mole of oxygen molecules contains oxygen molecules

O O16 16

32

32g

6.02 x 1023

How many moles in:

28 g of nitrogen molecules?80g of bromine molecules?5g of hydrogen molecules?

What is the weight of:

1 mole of chlorine molecules?½ mole of oxygen molecules?2 moles of ammonia (NH3) molecules?

1 mole0.5 moles2.5 moles

70g16g

34g

Compounds are just like molecules!

1 mol of a compound is the Relative Formula Mass in grams

Example: methane (CH4)

C12

H1

H1

H1

H1

Relative formula mass =

Mass of 1 mol of methane =

1 mol of methane contains methane molecules

16

16

6.02 x 1023