JJ Thomson
Albert
Einstein
Neils
Bohr
Earnest
Rutherford
HISTORY OF THE ATOM
JJ Thomson- Plum Pudding Model
Electrons are scattered throughout a positively
charged body.
DISCOVERY OF RADIATION
• Radioactive Material- unstable material that
emits high energy electromagnetic waves or
particles when broken down.
• Henri Becquerel-1896- discovered radiation is
emitted from uranium.
Marie Curie- isolated polonium and radium
• “Neither of us could foresee that in beginning this
work we were to enter the path of a new science
which we should follow for all our future.”
Ernest Rutherford-1911- determined
that there are 3 types of radiation
Alpha Particles (α)- Helium nucleus. ( 24He )
Beta Particle (β)- High speed electron (0-1e )
Gamma Rays (γ)-High energy electromagnetic
wave moving at the speed of light.
RUTHERFORD GOLD FOIL EXPERIMENT
-Alpha particles
GOLD FOIL EXPERIMENT
 Most particles passed through foil without
deflection. Indicated that the atom is
mostly empty space.
 Some particles were deflected backwards.
Indicated that the atom has a central (+)
mass.
 Few deflections occurred at large angles.
Indicated that the nucleus is small and
dense.
 Electrons don’t have enough mass OR
charge to change the path of the alpha
particle
RUTHERFORD MODEL OF THE ATOM
Small, dense,
positively charged
nucleus.
Electrons are located
outside the nucleus.
GOLD FOIL LIMITATIONS
Didn’t identify entire mass. (1932 Chadwick
found the neutron)
Didn’t explain why the electrons aren’t
attracted to the nucleus, which would cause
the atom to collapse.
Didn’t account for light emission as electrons
orbit.
Didn’t account for different spectrums of
light produced by different atoms.
Maxwell Planck-1900- Proposed
that light is an electromagnetic
wave that forms bundles of energy
called photons. This brought about
the idea of the dual nature of light
and led to further investigation of
the atom
Neils Bohr 1927
• Developed the planetary model of the atom
where the electrons orbit the nucleus in fixed
positions without radiating light.
Bohr Model
 The (+) nucleus and (-) electrons give the
atom its energy.
 As distance from the nucleus increases, more
energy is needed to hold electrons in orbit.
 Atoms emit a photon when an electron drops
to a lower energy level.
 Energy of the emitted photon is equal to the
change in energy levels.
Ionization energy- the energy needed to move
an electron to ground state. The (-) value
indicates the electron energy is controlled by
the nucleus.
On reference table
If electrons move
to a higher energy
level, they absorb a
photon.
If they drop to a
lower energy level
they give off energy
in the form of a light
wave.
Photon energy
Ephoton = Ei – Ef
Ei = initial level
Ef= final level
unit: eV (electronvolts) or J (joules)
1 eV= 1.6 x 10-19J
Ex- An electron falls from the 2nd energy level
to ground state of a hydrogen atom. If it gives
off a photon, what is the energy of the
photon?
Ephoton = -3.4eV − -13.6eV = 10.2ev
Ephoton = (10.2eV)(1.6 x 10-19 J/eV)
Ephoton = 1.63 x 10-18 J
Spectrum- the light
pattern given off
when a photon is
emitted.
Lyman Serieselectron moves to
ground state.
(ultraviolet range)
Balmer Serieselectron falls to 2nd
energy level.(visible
light)
Paschen Series- Electron
falls to the 3rd energy level
( Infrared range)
Bohr Model Limitations
Limited electrons to specific levels.
Didn’t explain how the electrons could have
centripetal acceleration without extra energy.
Goes against Newton’s Laws
DeBroglie Model-1924- Showed that the electrons
orbit the nucleus in a wave pattern. Doesn’t
account for electrons between orbitals
Cloud Model- Erwin Schrodinger- instead of
levels, electrons are located in areas of high or
low probability called energy states
Low
Probability
High
probability
Albert Einstein-1905
Proposed that the
mass of a body is the
measure of its energy
content. This could
help explain model
limitations and
showed a mass
discrimination in the
atom.
Einstein’s energy equation
E = m c2
E- energy (Joules)
m- mass (kg)
c- speed of light
3 x 108 m/s
celeritas (c) - extreme
swiftness
Ex) What is the energy content of a 70kg student?
E = 70kg(3x108)2
E = 6.3 x 1018 J
Ex) What is the mass of a subatomic
particle having 0.66eV of energy?
a) First convert eV to joules:
E= 0.66eV(1.6 x 10-19 J/eV)
E = 1.056 x 10-19 J
b) Then Use E=mc2 :
1.056 x 10-19 J = m (3x108m/s)2
m= 1.17 x 10-36 kg
Ex: What is the energy content of a
carbon atom in eV and Joules?
a) Atoms are measured in AMU (atomic mass
units)
1AMU= 931MeV
Carbon has a mass of 12 AMU
E= 12 AMU(931MeV/AMU)
E = 11,172 MeV
b) 1 MeV = 1x106eV
E= 11172MeV(1x106eV/MeV)
E = 1.1172 x 1010 eV
c) 1 eV = 1.6 x 10-19 J
E = 1.1172 x 1010 eV( 1.6x10-19 J/eV)
E = 1.78 x 10-9J