Download Chapter 3 Lecture - MRS. STOTTS CHEMISTRY

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CHAPTER 3
ATOMS & MOLES
What do we know?
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Atoms compose all ordinary matter
 To understand matter, we begin by
understanding atoms

What is an atom?
 An atom is the smallest identifiable unit
of an element.

Dalton’s Theory
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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?
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

Some of Dalton’s Theory about the
atom has been altered based on new
information
This gives us the …..
Modern Atomic Theory
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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.

How did we discover the parts of
the atom?
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
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
Thompson’s Cathode Ray Tube Experiment
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Discovering the charge of the
electron
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
Millikan’s Oil Drop Experiment
What
does it look like?
It weighs 9.109 x 10-31 kg
Why is the electron so important?
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The electron is a fundamental part of
how atoms chemical bond.
 The charge of the electron is important
because it determines how strongly an
atom holds its electrons

What about the Nucleus?
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Plum Pudding Model
Nuclear Model
Rutherford’s Gold Foil Experiment
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Fired alpha
particles (Helium)
through thin sheets
of gold
 Most particles went
completely through
 Few were deflected

Their conclusion …
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
The nucleus:
Small
Dense
(meaning heavy and packed)
Positively charged
Contains the protons and neutrons
What are the part of an atom?
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
Electrons
 Negatively
charged
 Outside of the nucleus

Protons
 Positively
charged
 Inside of the nucleus

Neutrons
 Charge:
Neutral
 Inside of the nucleus
Protons = Atomic Number
The number of protons
identifies the element
Electrons = # of protons
Neutrons = Atomic mass - Protons
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Atomic Number
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It represents the # of protons
 It can also represent the # of electrons
if the atom is neutral

Atomic Mass
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Represents the # of protons + # of
neutrons
 Neutrons by itself =
Atomic Mass – Atomic Number

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How to identify the parts on the
periodic table
Atomic
Number
Element
Symbol
Atomic mass
Element
Name
Practice:
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
Boron
 How
many protons?
 What is the atomic mass?
 How many neutrons?

Zinc
 How
many protons?
 What is the atomic mass?
 How many neutrons?
Quick Check #2
1.
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What is the difference between the two
diagrams below? Be specific, protons,
neutrons, electrons, charge, mass, etc
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Isotopes
Isotopes
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Atoms of the same element with different
masses
 Protons are the same
 Neutrons differ
 Notation: Chemical Symbol  uranium-235
Or
Nuclear Symbol

Atomic mass
Atomic number
235
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U
Element Symbol
Isotope Notation – Nuclear Symbol
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10 Neutrons
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10
Ne
11 Neutrons
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10
Ne
Symbol and Atomic
number are all the
same
12 Neutrons
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10
Ne
Practice:
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Ex. How many protons, electrons, and
neutrons are there in an atom of
chlorine-37?
How many protons, electrons, and
neutrons are there in an atom of
?
Quick Check 3
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
Which two are isotopes of each other?
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A. 82


X
208
B. 83
X
206 X
C. 82
207 X
D. 85
Explain your reasoning for picking the two.
Identify the element
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ATOMIC MASS: THE
AVERAGE MASS OF AN
ELEMENT’S ATOMS
Calculating the Average atomic mass
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
Practice:
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
Copper has two naturally occurring isotopes:
Cu-63 with mass 62.9396 and a natural
abundance of 69.17%, and Cu-65 with mass
64.9278 and a natural abundance of
30.83%. Calculate the atomic mass of
copper
Practice:
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
Naturally occurring chlorine consists of
75.77% chlorine-35 atoms with mass
34.97 and 24.23% chlorine 37 with
mass 36.97. Calculate the atomic mass
of chlorine
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THE MOLE & AVOGADRO’S
NUMBER
The Mole
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


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
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

The Number of particles in one mole of any
substance
6.022 x 1023 atoms / ions / particles / compounds
/ etc.
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YUP! MORE UNITS….. THAT MEANS
WE……
CONVERT!!!!
The Mole Map
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Solving Mol – g Problems
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Practice
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How many grams of He are there in
2.00 moles?
Practice
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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?
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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?
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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
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What is the mass in grams of 3.50
mol of copper, Cu?
Sample Problem C
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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
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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
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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
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A chemist produced 11.9 g of aluminum, Al. How
many moles of aluminum were produced?
Sample Problem D
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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
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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
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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
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NOW IT’S YOUR TURN ….
Mole Conversions # 1