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Subatomic Particles
Atomic Structure Timeline
ATOM
NUCLEUS
NUCLEUS
ELECTRONS
ELECTRONS
PROTONS
PROTONS
NEUTRONS
NEUTRONS
POSITIVE
POSITIVE
CHARGE
NEUTRAL
CHARGE
NEGATIVE
CHARGE
NEGATIVE CHARGE
QUARKS
John Dalton (1807)
John Dalton
Dalton’s Four Postulates
• British Schoolteacher
– based his theory on others’
experimental data
• Billiard Ball Model
– atom is a
uniform,
solid sphere
J. J. Thomson (1903)
• Cathode Ray Tube
Experiments
– beam of negative particles
• Discovered Electrons
– negative particles within
the atom
• Plum-pudding Model
1. Elements are composed of small indivisible
particles called atoms.
2. Atoms of the same element are identical.
Atoms of different elements are different.
3. Atoms of different elements combine together
in simple proportions to create a compound.
4. In a chemical reaction, atoms are rearranged,
but not changed.
J. J. Thomson (1903)
Plum-pudding Model
– positive sphere
(pudding) with
negative electrons
(plums) dispersed
throughout
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Ernest Rutherford (1911)
Ernest Rutherford (1911)
• Gold Foil Experiment
• Discovered the nucleus
– dense, positive charge in
the center of the atom
• Nuclear Model
• Nuclear Model
– dense, positive nucleus surrounded
by negative electrons
James Chadwick (1932)
James Chadwick (1932)
• Discovered neutrons
– neutral particles in the
nucleus of an atom
Neutron Model
• revision of Rutherford’s Nuclear Model
Niels Bohr (1913)
• Bright-Line Spectrum
Electrons in Atoms
– tried to explain presence
of specific colors in
hydrogen’s spectrum
• Energy Levels
– electrons can only exist in
specific energy states
• Planetary Model
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Niels Bohr (1913)
Bright-line spectrum
• Planetary Model
Erwin Schrödinger (1926)
• Quantum mechanics
– electrons can only exist in
specified energy states
• Electron cloud model
– orbital: region around the
nucleus where e- are likely
to be found
– electrons move in circular
orbits within specific
energy levels
Erwin Schrödinger (1926)
Quantum Mechanics
Electron Cloud Model (orbital)
• dots represent probability of finding an enot actual electrons
Quantum Theory
Quantum Theory
• Planck (1900)
– Observed - emission of light from hot objects
– Concluded - energy is
emitted in small, specific
amounts (quanta)
• Einstein (1905)
– Photon - particle of light that carries a
quantum of energy
– Quantum - minimum amount of energy
change
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Bohr Model
• e- exist only in orbits with specific
amounts of energy called energy levels
• Therefore…
– e- can only gain or lose certain amounts of
energy
– only certain photons are produced
Energy Levels
• Electrons can only exist at
certain energy levels.
• Low energy levels are close
to the nucleus.
• Each energy level can hold
only a certain amount of
electrons.
Bohr Model
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• Energy of photon
depends on the
difference in energy
levels
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2
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Waves
• Wavelength () - length of one complete
wave
• Frequency () - # of waves that pass a
point during a certain time period
– hertz (Hz)
Waves

H
I
G
H
L
O
W
crest
A
EM Spectrum
origin
A

trough
E
N
E
R
G
Y
red
R O Y
G.
orange
green
yellow
B
blue
I
indigo
V
violet
E
N
E
R
G
Y
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Planck’s constant
• Velocity of a Wave= frequency x wavelength
• E = fh
– Where,
– E= energy
– f= frequency
– h= 6.63 x 10-34
• V= f λ
• Speed of light= 3 x 108 m/s
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