1. Moles and Formula Mass H2O mole of H2O 6.02 × 1023 molecules of H2O
126 grams of H2O
18.0 grams of H2O
mole of H2O
Moles and
Formula Mass

2. Approximately 1 mole of Si
The atomic mass of an element is different than the mass number of an isotope.
28.1 grams of silicon
Approximately 1 mole of Si
The atomic mass is equal to the number of grams in 1 mole of an element.

3. Avogadro's constant = 6.02 × 1023 particles/mole
A mole (mol) is a unit of measurement in chemistry that allows us to express the amount of a substance.
Because atoms are so small, we use a very large number to talk about them. This number is known as Avogadro's constant.
Avogadro's constant = 6.02 × 1023 particles/mole
6.02 × 1023 particles is known
as a mole of particles

4. The amount of mass an object has is directly related to the number of particles and the size of each particle that are inside of it.
Which sample below has the greatest mass?
9 iron atoms
8 iron atoms
8 iron atoms
Sample 1
Sample 2
Sample 3

5. Which sample below has the greatest mass?
The size of each particle affects the total mass

6. Fighting crime one extensive property at a time!
Since moles and number of particles are based on the size/amount of a sample, they are extensive properties!
MVL MEN
The
Extender
XXL M V L E N
ass
olume
ength
oles
Captain Extreme
nergy
Fighting crime one extensive property at a time!
umber of particles

7. The atomic mass is the mass of 1 mole of that specific element.
Because different elements have different masses, scientists have studied each element to determine how much mass 6.02 × 1023 atoms of an element would have.
The atomic mass is the mass of
1 mole of that specific element.

8. Covalent compounds are made of MOLECULES.
If the substance is an element, the smallest particle is called an ATOM.
Covalent compounds are made of MOLECULES.
Ionic compounds are made of SALTS. We call the theoretical single unit a FORMULA UNIT.
Silicon
Water
Sodium Chloride
Formula Unit
Silicon Atom
Water Molecules
Salt Crystal

9. Every compound has a formula.
In a covalent compound, the formula represents the ratio of atoms in each molecule.
In an ionic compound, the formula represents the ratio of atoms that are in the crystal.
H2O
NaCl

10. On your notes, decide what the ratio of elements would be in the smallest unit of each compound.2 1 1 2 1 2 1 3 1 1 1 5 6 12 6 1 1 1 1 1 1 3 1 1 4

11. To find the formula mass of a compound, you simply add together the masses of each compound.
(You can round to the nearest tenth.)
NaCl
formula mass of NaCl = 23.0 g g = 58.5 g
H2O
formula mass of H2O = 1.0 g g g = 18.0 g

12. Notice that since there were two hydrogen atoms in water, we added it twice.
H2O
formula mass = 1.0 g g g = 18.0 g

13. What is the formula mass of carbon dioxide?
(You can round to the nearest tenth.)
CO2
formula mass of CO2= 12.0 g g g = 44.0 g
You have to understand that this is the mass of
1 mole of this compound!

14. Determine the formula mass of each of the compounds on your notes.
14.0g + 1.0g + 1.0g + 1.0g = 17.0g
24.3g g g = 184.1g
63.5g g + 4(16.0g) = 159.6g
23.0g g = 58.5g
6(12.0g) + 12(1.0g) + 6(16.0g) = 180.0g
31.0g + 5(79.9g) = 430.5g

15. There are 7 elements that exist in nature as diatomic molecules.
Diatomic means 2 atoms.
The 7 diatomic molecules:
H2, N2, O2, F2, Cl2, Br2, I2 O2
32.0 grams
mole

16. Now your teacher will show you how to convert between grams and moles of a substance.