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4.1 Defining the Atom
Early Models
Democritus (about 400BC)matter composed of tiny,
indivisible particles
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Dalton (about 1800)- - used scientific
method
transformed Democritus’ ideas
into theory
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4.1 Defining the Atom
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Atoms of element A are identical
Atoms of
element B
are
identical,
but
different
than
A and BA
element
Atoms of
element A and B can be
can be physically chemically
combined
mixed together
as a
compound
Dalton Proposed
1.All elements composed of tiny, indivisible
particles
2. Atoms of an element are identical &
distinct from atoms of other elements
3. Atoms can form compounds, combining in
simple whole-number ratios
4. Atoms can be rearranged (chemical
reactions), but atoms of one element do
not change into atoms of another
element.
Sizing Up the Atom
5x10-11 - 2x10-10m
Atoms cannot be seen
with a light microscope
A tunnelling electron
microscope can make
images of atoms like
this:
Tunnelling
Electron
Microscope
Atoms cannot
be seen with a
light
microscope
Tunnelling Electron Microscope
Atoms cannot be seen with a light
microscope
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Chemistry Warm Up Chapter 4 Scavenger Hunt.
1. Copy this table and fill in the missing information:
Name of
Particle
Mass Relative Charge
to a Proton
Location in
the Atom
2. Given that 1 mile = 5280 feet,
Use conversion factors and dimensional analysis to calculate the number of
miles in 12 427 inches.
Show all your work, conversion factors and proper cross-canceling of units.
Chemistry Warm Up Chapter 7 Scavenger Hunt.
1. Copy this table and fill in the missing information:
Name of
Particle
Mass Relative Charge
to a Proton
Location in
the Atom
Proton
1
1+
Nucleus
Neutron
>1
0
Nucleus
1-
Around
nucleus
Electron
1/1840
2. Given that 1 mile = 5280 feet,
Use conversion factors and dimensional analysis to calculate the number of
miles in 12 427 inches.
Show all your work, conversion factors and proper cross-canceling of units.
Chemistry WarmUp Copy ALL of these assignments into your binder
Including dates, WarmUps, InClass assignments AND page numbers!
September 28-29
WarmUp:
Agenda / Isotope Introduction
InClass: The Black Box p108
Demo: Observing Cathode Rays p105TE
InClass Periodic Table 101
Homework Key Concepts 4.2 and 4.3 DUE NEXT CLASS
September 30
WarmUp: questions q21-24p116-117
InClass: Dimensional Analysis Practice
Homework: Complete notes 5.1 answer q1-7p132 DUE NEXT CLASS
October 1-2
WarmUp: Ms Lyall’s Periodic Table Scavenger Hunt
Test: Chapters 1-3
InClass: The Wintergreen Lifesaver Effect. Urban Legend? We find out.
InClass: Electron Configuration Worksheet
Demo: Atomic Emission Spectra p137 (adapted)
Homework: Complete notes 5.2 answer q8-9p135 DUE NEXT CLASS
When you finish, read 4.2 and complete your notes.
4.2 Structure of the Nuclear Atom
Subatomic Particles
Atoms not indivisible
Electrons
Protons
Neutrons
Electrons
Discovered 1897
by J.J.Thomson
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Used cathode
ray tube to
show electrons
are negatively
charged
Electrons
Discovered 1897 by J.J.Thomson
Used cathode ray tube to show
electrons are negatively charged
Deflected
by magnet
Electrons
Discovered 1897 by J.J.Thomson
Used cathode ray tube to show
electrons are negatively charged
Deflected by
electrical
charge
Electrons
Discovered 1897 by J.J.Thomson
Calculated charge/mass ratio
The ratio of charge to mass
was the same, regardless of
gas in cathode tube.
Conclusion? Electrons must
be present and the same in
all elements.
Electrons
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Electrons
Robert A Millikan 1916 oil drop experiment
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Millikan calculated the mass of an electron
Mass or electron = 1/1840 mass of a
hydrogen atom
Charge = -1
Electrons
Robert A Millikan 1916 oil drop
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experiment
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The actual apparatus used in the Millikan
oil drop experiment
Neutrons and Protons
Atoms are neutral
When charges do exist, they are always in
simple multiples of the charge on an electron
(no fractions)
Eugen Goldstein 1886 found cathode ray
evidence of protons
Proton- charge of +1
mass 1840 times mass of electron
(1 atomic mass unit)
Neutrons and Protons
Neutrons
Not discovered until 1932
by James Chadwick
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Neutrons have no charge
have a mass similar to proton
Atomic Nucleus
“Plum pudding,” model
Electron, “raisins,” stuck in a
lump of positive, “dough.”
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Disproved in
1911 by one of
Thomson’s
students,
Ernest
Rutherford
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Rutherford’s Gold Foil Experiment
Alpha particles shot at
a thin piece of gold
foil did not pass right
through with slight
deflection. Instead,
most passed
straight through.
Some bounced right
back!
Rutherford’s Gold Foil Experiment
Rutherford concluded that
•Most of the atom is empty space
•All of the positive charge
and almost all of the mass is
Concentrated in the tiny core, “nucleus.”
composed of protons and neutrons.
An idea of the size:
Atom = football stadium
Nucleus = marble
4.3 Distinguishing Atoms
Atomic number = number of protons
Defines the element!
Atoms are electrically neutral
therefore atomic number also is the
number of electrons
p111 problem 15
15 complete the table:
Element
Atomic #
Protons
K
19
19
19
B
5
5
5
S
16
16
16
V
23
23
Electrons
23
p111 problem 16
16 How many protons and electrons?
a.Fluorine
9
b. Calcium
20
c. Aluminium
13
(Atomic) Mass Number
number of protons + number of neutrons
= mass number
Therefore
mass number - number of protons
= number of neutrons
Helium with a mass number of 4 has 2
protons. How many neutrons does it
2 neutrons
have?
Isotope Notation
mass number
(number of protons
+ neutrons)
197
79
Au
symbol
First letter always
capitalized
Second letter never
capitalized
atomic number
(number of protons)
How many neutrons does an
atom of gold-197 have?
118 neutrons
How many neutrons
p112 q17
a.
16
8
O
b.
8 neutrons
d.
32
16
S
c.
108
47
61 neutrons
16 neutrons
80
35
Br
45 neutrons
e.
Ag
207
82
Pb
125 neutrons
Express in Isotope
Notation p112 q18
a. Carbon-12
12
6
C
F
a. Fluorine-19
19
9
a. Beryllium-9
9
4
Be
Express in Isotope
Notation p112 q18
a. Carbon-12
12
6
C
F
a. Fluorine-19
19
9
a. Beryllium-9
9
4
Be
Isotopes
20
Neon-20
Neon-21
Neon-22
Ne
21
10 Ne
22
10 Ne
10
10 neutrons
11 neutrons
12 neutrons
Isotopes have
different #
of neutrons,
same # of
protons and
electrons
Q19 p113
Use isotope notation to show
Oxygen-16
16
8
O
Oxygen-17
17
8
O
Oxygen 18
18
8
O
Q12
How many neutrons in each?(Chromium’s atomic number=24)
Chromium-50
26 neutrons
Chromium-52
28 neutrons
Chromium-53
29 neutrons
Atomic Mass
Atomic Mass Unit
1/12 mass of an atom of carbon-12
Since carbon 12 has 6 protons
and 6 neutrons,
Mass of 1 proton is about 1amu
Why isn’t the atomic mass =
atomic mass number?
Atomic Mass
Weighted average of the mass of all
naturally occurring isotopes.
To find atomic mass, calculate
(Mass of isotope)•(%abundance as decimal)
For each isotope
And add the results together
Atomic Mass
Carbon is
98.89% Carbon-12 &
1.11% Carbon-13
Its atomic mass would be
(12amu•0.9889)+(13.03amu•0.0111) =
12.011 amu
Chemistry Warm Up
questions q21-24p116-117
You CAN do this. Work out the example if you
are stuck. It’s like this:
Carbon is made up of
98.89% Carbon-12 &
1.11% Carbon-13
Its atomic mass would be
(12amu•0.9889)+(13.03amu•0.0111) =
12.011 amu
Chemistry Warm Up
questions q22-24 p149
Try to answer these without your notes or the
book,
then go back and check your answers against
your notes or the book.
When you finish, complete the second version
of
Reading & Processing Information from the
Periodic Table (worksheet)
Chapter 4 Review
1. Make a sketch of an atom of Lithium-6. Label the 3 main subatomic
particles.
2. What is the mass number of the atom you drew in question 1? How do
you know?
3. Invent an isotope of the atom you drew above make a labeled drawing
of it. How do you know it is an isotope?
4. Make a labeled drawing of Thomson’s cathode ray tube experiment.
What did he discover?
5. Make a labeled drawing of Rutherford’s gold foil experiment. What
important hypothesis did Rutherford propose?
6. What is an atomic mass unit?
7. Based on the correct answer to question 6, one might expect carbon’s
atomic mass to be 12.000. Why does the periodic table list carbon’s
atomic mass as 12.011?
8. Show, with an example, how atomic mass is calculated.
Chapter 4 Review Worksheet
1. Make a sketch of an atom of Lithium-6. Label the 3 main subatomic
particles.
Chapter 4 Review Worksheet
2. What is the mass number of the atom you drew in question 1? How do
you know?
The mass number is 3.
All lithium has 3 protons. That’s its atomic number.
Lithium-6 has a mass number of 6.
The mass number is the number of protons + neutrons.
6 protons + neutrons - 3 protons = 3 neutrons
3. Invent an isotope of the atom you drew above make a labeled drawing
of it. How do you know it is an isotope?
An isotope has the same atomic number with a different number of
neutrons (therefore a different mass number).
Chapter 4 Review Worksheet
4. Make a labeled drawing of Thomson’s cathode ray tube experiment.
What did he discover?
Thomson is credited with discovering a very, very small sub atomic
particle with a negative charge, the electron.
Chapter 4 Review Worksheet
5. Make a labeled drawing of Rutherford’s gold foil experiment. What
important hypothesis did Rutherford propose?
Rutherford is credited with discovering the nuclear atom.
His hypothesis is that the atom contains a relatively small nucleus
which contains all of the positive charge and almost all of the mass of
the atom.
Chapter 4 Review Worksheet
6. What is an atomic mass unit?
An atomic mass unit is equal to 1/12 the mass of an atom of carbon12.
Chapter 4 Review Worksheet
7. Based on the correct answer to question 6, one might expect carbon’s
atomic mass to be 12.000. Why does the periodic table list carbon’s
atomic mass as 12.011?
Atomic mass takes into account all the isotopes of an element.
Atomic mass is the weighted average of all the naturally occuring
isotopes of an element.
8. Show, with an example, how atomic mass is calculated.
(12.00amu x .99) + (13.00amu x 0.01) = 12.01amu
Periodic
Table
Horizontal row = period
Atomic number increases left to right
Atomic number increases as you go
down
Properties vary as you go across a
period
Vertical column = group
Groups have similar chemical properties