Download Early atomic theory • The Greek philosophers (400 BC) –Democritus

Early atomic theory
• The Greek philosophers (400 BC)
–Democritus
–Aristotle
9
“New” atomic theory
• John Dalton (early 1800
1800’s)
s)
–Proposed first atomic theory
b k d with
backed
h experimentall
evidence.
10
“New” atomic theory
• John Dalton (early 1800
1800’s)
s)
–Studied the work of Antoine
Lavoisier and Joseph Proust
–Lavoisier – law of conservation of
mass
–Proust – law of definite
proportions (ratio of masses)
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“New” atomic theory
• John Dalton (early 1800
1800’s)
s)
–Proposed the law of multiple
proportions
–Explained
Explained a few years later by
Amadeo Avagadro
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Dalton’s atomic theory
• John Dalton (early 1800
1800’s)
s)
–All matter is composed of atoms,
which
h h are the
h smallest
ll
possible
bl
p
particle.
13
Dalton’s atomic theory
• John Dalton (early 1800
1800’s)
s)
–All atoms of the same element
are identical.
d
l
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Dalton’s atomic theory
• John Dalton (early 1800
1800’s)
s)
–Atoms combine in simple whole
number
b ratios.
15
“New” atomic theory
• Dalton’s
Dalton s work
–Since been tested and proved
correct
–As
As new discoveries happened,
major revisions have occurred.
16
Modern atomic theory
•J
J.J.
J Thomson (1897)
–Cathode ray tube
–Discovered
Di
d th
the electron
l t
–Changed
g gas
g in tube and
concluded all contained the
p
particle
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Modern atomic theory
18
Modern atomic theory
•J
J.J.
J Thomson (1897)
–Calculated the charge to mass
ratio of
f an electron
l
–Won
Won the Nobel Prize in Physics in
1906 for his work.
22
Modern atomic theory
• Robert Millikan (1916)
–Performed the oil drop
experiment
–Discovered
Discovered the actual mass of an
electron, then the charge using
Thomson’ss work.
Thomson
work
23
Modern atomic theory
24
Modern atomic theory
• Robert Millikan (1916)
–Won the Nobel Prize in Physics in
1923 for
f h
his work
k
25
Modern atomic theory
• Since the atom has a negative
particle, it was not a big leap to
conclude it must have a positive one
as well.
• Why?
26
Modern atomic theory
• Ernest Goldstein (1897)
–Discovered the proton
27
Modern atomic theory
• The proton and electron were found
to have an identical charge, only
opposite
pp sit in sign.
si n
28
Modern atomic theory
• A third particle would go
undiscovered for some time,
although
lth
h it wass predicted
p di t d to
t exist
xist
by Lord Rutherford in 1920.
29
Modern atomic theory
• James Chadwick (1932)
–Discovered the neutron
–It is equal in mass to a proton,
but has no charge
30
Modern atomic theory
• These discoveries lead us to the
first major revision to Dalton’s
atomic
t mi th
theory.
31
Modern atomic theory
• Dalton stated that atoms are the
smallest possible particle. Not true!
• They are made up of protons,
protons
neutrons, and electrons.
32
Modern atomic theory
• These newly discovered particles
are called sub-atomic particles.
33
Models of the atom
• Once these sub-atomic particles
had been discovered, scientists
st t d tto wonder
started
nd h
how they
th fit
together.
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The atom
• More on this later…
later
• Some more facts about atoms…
35
The atom
• While working with Neon,
Neon Thomson
found two kinds of Neon atoms.
Th were alike
They
lik chemically,
h mi ll but
b t had
h d
different masses.
36
The atom
• We now know these are called
isotopes.
• Isotopes are atoms of
f the
h same
element with different masses.
37
The atom
• By the mid-1800
mid-1800’ss, about 70
elements had been discovered and
s i ntists were llooking
scientists
kin f
for a way tto
organize them.
39
The atom
• Dimitri Mendeleev
–Known as the father of the
periodic table
–Arrange his table according to
atomic
t i mass
–Left blank spaces
p
for
undiscovered elements
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The atom
• Dimitri Mendeleev
–Problems- Co and Ni, Te and I, Ar
and
dK
41
The atom
• Henry Moseley (1913)
–Studied the x-rays produced by
d ff
different
metals
l in an x-ray tube
b
–Discovered
Discovered atomic number
42
The atom
• Atomic number is the number of
protons in an atom’s nucleus.
• It determines
d
the
h identity
d
of
f an
element.
43
The atom
• The periodic table is organized
according to increasing atomic
n mb
number.
periodic law.
• Called the p
44
The atom
• Another revision to Dalton’s
Dalton s atomic
theory:
• Atoms of one element contain the
same number of protons, but can
contain different numbers of
neutrons.
• Isotopes!
I t
!
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Isotopes
• Another name for an isotope is a
nuclide.
• Nucleons are particles that make up
the nucleus.
• Mass
M
number
b is
i the
th number
b of
f
nucleons.
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I t
Isotope
# #
Atomic
of
f of
f
#
p+ e -
#
Mass
of
f
#
0
n
Lithium-8
92
238
19
22
8
18
47
I t
Isotope
# #
Atomic
of
f of
f
#
p+ e 11
#
Mass
of
f
#
0
n
14
92
235
98
T
43 Tc
87 136
49
I t
Isotope
# # #
Atomic
Mass
of
f of
f of
f
#
#
+
0
p e n
8
14
79
102
238
T
Tc
81 136
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Models of the atom
• Now scientist began to wonder how
do these protons, electrons, and
n t ns fit ttogether.
neutrons
th
52
Dalton (1803)
• Remember Dalton believed atoms
were indivisible. So his model was a
s lid sph
solid
sphere.
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Dalton
54
J.J. Thomson (1897)
• Thomson discovered the electron,
electron
so he amended Dalton’s model to
in l d th
include
the electrons.
l t ns
55
J.J. Thomson (1897)
• It is called the plum-pudding model
model.
• Better analogy- like raisins stuck on
the
h surface
f
of
fab
ball
ll of
f dough.
d
h
56
Models of the atom
57
Rutherford (1909)
• Performed the gold foil experiment.
experiment
58
Rutherford (1909)
59
Predicted to happen
60
Actually happened
61
Rutherford’s quote
• ” It was about as credible as if you
had fired a 15-inch artillery shell at
a piece
pi
of
f tissue
tiss paper,
p p
and
nd it came
m
back and hit you.”
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Rutherford
• The two major finding of
Rutherford through the gold foil
experiment:
1. The atom is mostly empty space
2 It contains
2.
t i a positively
iti l charged
h
d
nucleus.
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Rutherford
65
Bohr (1913)
• Neils Bohr was a student of
Rutherford’s. He proposed the
pl n t
planetary
model.
m d l It st
states
t s th
thatt
the electrons revolve around the
nucleus
l
in set orbits.
66
Bohr (1913)
• These orbits can be viewed like
the rungs of a ladder.
• The
h electron
l
can move from
f
one
orbit to another, but cannot exist
in between orbits.
67
Bohr (1913)
• This is a statement of the
quantum theory, the idea that not
all
ll values
l s of
f energy
n
exist,
xist only
nl
certain values.
68
Bohr (1913)
• The rungs of the “ladder”
ladder are
not equally spaced.
• The
Th f
farther
th from
f
the
th nucleus,
l
the closer the rungs are to each
other,
th
the
th less
l
energy needed
d d to
t
jump to the next level.
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Bohr (1913)
70
Schrodinger (1926)
• Schrodinger took Bohr
Bohr’ss model
one step farther.
• He used the newly developing
quantum theory to wr
write
te
mathematical equations to
explain all possible locations of
the electron in a hydrogen atom.
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Schrodinger (1926)
• His model was quantized,
quantized like
Bohr’s model, but the orbits
were not as defined.
defined
• His equation could be solved for
all
ll probable
b bl llocations
ti
f
for an
electron.
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Schrodinger (1926)
• These probable locations would
give an electron density
di ib i resulting
distribution
l i iin an
electron cloud.
• The darker the cloud, the more
probable the location.
location
73
Schrodinger (1926)
• It is called the quantum
mechanical model, or electron
cloud
l d model.
d l
• This
h s iss still
st ll accepted today.
74
Schrodinger (1926)
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