Download Particles, Nuclei, and Isotopes

Particles, Nuclei, and Isotopes
The Nuts and Bolts of
Chemistry
Atomic History: An Overview
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Early Greeks - Democritus vs Aristotle
Dalton’s Atomic Theory
Thomson - discovery of electrons
Rutherford - discovery of nucleus
Chadwick - discovery of neutron
Bohr - planetary model of atom
Atomic History: An Overview
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Early Greeks - Democritus vs. Aristotle
Dalton’s Atomic Theory
Thomson - discovery of electrons
Rutherford - discovery of nucleus
Chadwick - discovery of neutron
Bohr - planetary model of atom
Early Greeks
• What is the nature of matter?
-Infinitely divisible pieces of “stuff”
-Earth, Air, Fire ,and Water
• No experiments
Early Greeks
Democritus vs. Aristotle
• Democritus
• Aristotle
• New idea
• “atomos” - indivisible
• Eventually, can’t
divide matter any
more
• First “atomic theory”
• Didn’t buy it…
• All things are
infinitely divisible
Guess who won?
(Aristotle)
For 2000 years,
scientists thought all
matter was infinitely
divisible…
Atomic History: An Overview
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Early Greeks - Democritus vs Aristotle
Dalton’s Atomic Theory
Thomson - discovery of electrons
Rutherford - discovery of nucleus
Chadwick - discovery of neutron
Bohr - planetary model of atom
Dalton’s Atomic Theory
John Dalton
• 1807
• Idea of “atom”
– Solid spheres that
were indestructible
– Unique to each
element
– Combine evenly
– Reactions are
rearrangements
Dalton’s Atomic Theory
• Atoms combine evenly in compounds
– Small, whole number proportions
– (e.g.) water - H20 (not H1O1/2 )
H
H
O
H
O
H
Atomic History: An Overview
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Dalton’s Atomic Theory
Thomson - discovery of electrons
Rutherford - discovery of nucleus
Chadwick - discovery of neutron
Bohr - planetary model of atom
Thomson’s Discovery
J.J. Thomson 1897
• Studied electricity not atomic
structure
• His 1st observation was that
a magnet could deflect the
current and realized that it
was made of particles
• So to study current he
pumped all the air out of a
glass tube and applied
voltage to two metal plates +
(anode)/- (cathode)
Thomson’s Discovery (cont…)
J.J. Thomson 1897
• He then sent a ray of particles
through the tube and saw that
they came out of the cathode
side and were attracted to the
anode side and the tube
glowed
• This told him that the particles
were negative… he called his
discovery a Cathode Ray Tube
– Sends a “ray” of - particles
– Used in TVs and Computers
Thomson’s Discovery
• The beam was attracted to the positive plate.
• So, cathode rays are negative
• He realized that these negative particle must be
ELECTRONS
Thomson’s Discovery
• Most books give Thomson credit for
discovering the proton
• He and Millikan found the mass of an
electron to be much smaller than an
atom
• So, electrons are VERY VERY small
• Protons must be large in comparison
– Plum Pudding Model
Plum Pudding Model
Preface: “Plum Pudding” atomic model
• atoms are solid
• made of positively-charged material
• with negative “bits” scattered throughout
(like raisins in plum pudding)
(or raisin bread)
Atomic History: An Overview
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Dalton’s Atomic Theory
Thomson - discovery of electrons
Rutherford - discovery of nucleus
Chadwick - discovery of neutron
Bohr - planetary model of atom
Rutherford’s Discovery
Ernest Rutherford
Image courtesty of
http://www.nobel.se/chemistry/laureates/1908/rutherford-bio.html
Gold Foil Experiment
To test the Plum Pudding Model (1907):
• Shot alpha rays at thin gold foil
– (about 2000 atoms thick)
• EXPECTED to see the ray scatter as it
hit all the solid positive atoms
– Like spray from a nozzle
Gold Foil Experiment
Here is what they saw:
Gold Foil Experiment
In Detail:
Click here to
see an
animation.
Gold Foil Experiment
RESULTS
• Most of the particles were not deflected
• Some were minimally deflected
• VERY few (1 in 20,000) bounced back
– “as if you had fired a 15-inch shell at a
piece of tissue paper and it came back and
hit you.” Rutherford
Gold Foil Experiment
CONCLUSIONS
• Plum pudding model wrong
• A “nucleus” exists
– It is tiny
– It is densely-packed and positively-charged
(this is the only way a strong positive
particle could be deflected)
• Empty spaces exist in atoms
– LOTS of it!!!!
Gold Foil Experiment
How much empty space?
• Use a billiard ball to represent a nucleus
• The electrons occupy a volume one
kilometer in ALL DIRECTIONS
• Most of that space is EMPTY.
Atomic History: An Overview
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Dalton’s Atomic Theory
Thomson - discovery of electrons
Rutherford - discovery of nucleus
Chadwick - discovery of neutron
Bohr - planetary model of atom
Chadwick’s Discovery (1932)
Chadwick
• PROBLEM
• There was more
mass in nucleus
than explained by
protons alone
• Where did it come
from?
• NEUTRONS
Atomic History: An Overview
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Dalton’s Atomic Theory
Thomson - discovery of electrons
Rutherford - discovery of nucleus
Chadwick - discovery of neutron
Bohr - planetary model of atom
Bohr’s Atomic Model
• Nucleus has +
charge
• Electrons have charge
• Why don’t electrons
simply “fall into” the
nucleus?
Bohr
Bohr’s Atomic Model
• Bohr pictured atoms as
little solar systems
• Nucleus in center
• Electrons “orbiting” in
circles
–We now know this isn’t
correct
–But it helps to explain many
things about atoms
What Theory Do We Currently
Support?
• Electron Cloud Model
– Nucleus is composed of Protons and
Neutrons
– Electrons spin very quickly around the
nucleus forming a “giant cloud” of negative
energy
– These electrons can move further away or
closer to the nucleus at anytime
– Their distance and space is infinite!
HOMEWORK
Notes 4.2
Protons, Neutrons, and Electrons
Three Main Subatomic Particles
• Protons
– Located in nucleus
– Positively charged (+1)
– Mass = “1” mass unit (or 1 gram/mole)
• Number of protons = atomic number (Z)
Protons, Neutrons, and Electrons
Three Main Subatomic Particles
• Neutrons
– Located in nucleus
– no charge (0)
– Mass = “1” mass unit (or 1 gram/mole)
Protons, Neutrons, and Electrons
Three Main Subatomic Particles
• Electrons
– Located outside nucleus
– negative charge (-1)
– So small we assume mass = 0
• Actual mass of 0.000 5 g/mol
Protons, Neutrons, and Electrons
Atomic number (Z)
• shown in lower left
• ALWAYS equals the
number of protons
• Equals the number
of electrons in a
neutral atom
Isotope Notation
C
6
Protons, Neutrons, and Electrons
Mass Number (A)
• shown in upper left
• Is the sum:
neutrons + protons
• In this example,
carbon has 6 protons
and 7 neutrons
Isotope Notation
C
13
6
Protons, Neutrons, and Electrons
We call this atom
“carbon-13”
Isotope Notation
C
13
6
Protons, Neutrons, and Electrons
• Atoms with the same number of
protons can have different numbers of
neutrons.
• We call such atoms isotopes
Protons, Neutrons, and Electrons
• Atoms with the same number of
protons can have different numbers of
neutrons.
• We call such atoms isotopes
12
13
14
C
6
carbon -12
C
6
carbon -13
C
6
carbon -14
Protons, Neutrons, and Electrons
C
C
C
12
13
14
6
6
6
6 protons
6 electrons
6 neutrons
6 protons
6 electrons
7 neutrons
6 protons
6 electrons
8 neutrons
All three kinds of carbon atoms have the same chemistry!
Protons, Neutrons, and Electrons
1
1
H
1 proton
1 electron
0 neutrons
208
82
Pb
+2 19
82 protons
80 electrons
126 neutrons
9
F
9 protons
9 electrons
10 neutrons
Neutrons = A - Z Neutrons = A - Z Neutrons = A - Z
1-1=0
208 - 82 = 126
19 - 9 = 10
Protons, Neutrons, and Electrons
7
3
?
What element is this?
How do you know?
Protons, Neutrons, and Electrons
7
3
Li
What element is this? Lithium
How do you know?
the atomic number is 3
look on the periodic table
Protons, Neutrons, and Electrons
207
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Pb
235
92
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19
K
# of protons (Z)
82
92
19
# of neutrons
125
143
21
# of electrons
82
92
19
mass number (A)
207
235
40
lead-207
uranium-235
potassium-40
name
Homework…
Complete the
Atomic Structure Worksheets
((((( Back AND Front )))))