LECTURE 3
ATOMS & MOLES
It all starts with…..
The Law of Conservation of Mass
Mass is neither created nor destroyed in a
chemical reaction
Huh?
You can’t make stuff up or make it go
away just because you want to
“Stuff” just gets moved around
Chapter 3
Section 1 Substances Are Made
of Atoms
Law of Conservation of Mass
Chapter 3
Visual Concepts
Law of Conservation of Mass
Chapter 3
Section 1 Substances Are Made
of Atoms
Law of Conservation of Mass,
continued
Dalton’s Theory
All matter is made up of tiny particles
called atoms
Atoms of the same element are
identical in size, mass, properties
Atoms cannot be subdivided, created or
destroyed
Atoms of different elements combine to
form chemical compounds
How much of this is true?
Some of Dalton’s Theory about the
atom has been altered based on new
information
This gives us the …..
Modern Atomic Theory
All matter is made up of atoms.
Atoms of the same element are
chemically similar
Atoms of an element may not have the
same mass (Isotopes)
Atoms are not subdivided, created or
destroyed in chemical reactions.
Chapter 3
Visual Concepts
Isotopes and Nuclides
Isotopes
Atoms of the same element with
different masses
Protons are the same
Neutrons differ
Looks like: uranium-235
Or
235
92
U
What else do we know?
Discovering the Electron
Cathode Ray Tube
Produces a charged ray
When a positive magnet is placed near the
ray, the ray bends towards the + magnet
Thomson determined the electron was
negative
Chapter 3
Visual Concepts
Thompson’s Cathode Ray Tube
Experiment
Discovering the Electron
Millikan’s Oil Drop Experiment
What does it look like?
It weighs 9.109 x 10-31 kg
What about the Nucleus?
Fired alpha particles
(Helium) through
thin sheets of gold
Most particles went
completely through
Few were deflected
Chapter 3
Visual Concepts
Rutherford’s Gold Foil
Experiment
Their conclusion …
The nucleus:
Small
Dense (meaning heavy and packed)
Positively charged
Contains the protons and neutrons
In summary…
Chapter 3
Visual Concepts
Comparing Models of Atoms
Which picture is more accurate?
Chapter 3
Visual Concepts
Parts of an Atom
Atomic Number
It represents the # of protons
It can also represent the # of electrons
if the atom is neutral
Mass Number
Represents the # of protons + # of
neutrons
Neutrons by itself =
Mass Number – Atomic Number
Reviewing the Numbers
Atomic
Number
Reviewing the Numbers
Mass
Number
Sample Problem A
How many protons, electrons, and
neutrons are there in an atom of
chlorine-37?
Sample Problem A
How many protons, electrons, and
neutrons are there in an atom of
chlorine-37?
Protons
Electrons
Neutrons
Atomic #
Atomic #
Mass # Atomic #
?
?
?
Sample Problem A
How many protons, electrons, and
neutrons are there in an atom of
chlorine-37?
Protons
Electrons
Neutrons
Atomic #
Atomic #
Mass # Atomic #
17
17
20
Now it’s your turn …
Atomic Math Worksheet
The Mole & Avogadro’s
Number
The Mole
The amount of any substance that
contains the same number of particles
found in 12 g of Carbon-12
It’s a unit
Abbreviate “mol”
Avogadro’s Number
The Number of particles in one mole of
any substance
6.022 x 1023 atoms / ions / particles /
compounds / etc.
Yup! More units….. That means we……
CONVERT!!!!
The Mole Map
Solving Mol – g Problems
Sample Problem B
How many grams of He are there
in 2.00 moles?
Sample Problem B
How many grams of He are there
in 2.00 moles?
Step 1:
Start with what you know from the problem.
2.00 mol He
Sample Problem B
How many grams of He are there
in 2.00 moles?
Step 2:
What is the mass of He? (Look at the P.T.)
4.00 g / mol He
Sample Problem B
How many grams of He are there
in 2.00 moles?
Step 3:
Set-up the problem so the units cancel out.
4.00 g He
2.00 mol He 
= 8.00 g He
1 mol He
Sample Problem C
What is the mass in grams of
3.50 mol of copper, Cu?
Sample Problem C
What is the mass in grams of
3.50 mol of copper, Cu?
Step 1:
Start with what you know from the problem.
3.50 mol Cu
Sample Problem C
What is the mass in grams of
3.50 mol of copper, Cu?
Step 2:
What is the mass of Cu? (Look at P.T.)
63.55 g / mol
Sample Problem C
What is the mass in grams of
3.50 mol of copper, Cu?
Step 3:
Set-up the problem so the units cancel out.
63.55 g Cu
3.50 mol Cu 
= 222 g Cu
1 mol Cu
Sample Problem D
A chemist produced 11.9 g of aluminum,
Al. How many moles of aluminum were
produced?
Sample Problem D
A chemist produced 11.9 g of aluminum,
Al. How many moles of aluminum were
produced?
Step 1:
Start with what you know from the
problem.
Sample Problem D
A chemist produced 11.9 g of aluminum,
Al. How many moles of aluminum were
produced?
Step 2:
What is the mass of Al?
26.98 g / mol Al
Sample Problem D
A chemist produced 11.9 g of aluminum,
Al. How many moles of aluminum were
produced?
Step 3:
Set-up the problem so units cancel
out.
1 mol Al
11.9 g Al 
= 0.441 mol Al
26.98 g Al
Now it’s your turn ….
Mole Conversions # 1