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The Parts of an
Atom
J.J. Thomson
• He experimented with cathode ray
tubes
• He passed electricity through
the tube and discovered the
first subatomic particle – the
electron
• He developed the plum pudding
model of an atom
Plum Pudding Model
Robert Millikan
• He determined that the
electron has a negative
charge
• He determined the mass of
the electron
Ernest Rutherford
• He proved the plum pudding
model was incorrect with the
gold foil experiment
Gold Foil Experiment
positive
alpha
particles
• He discovered the nucleus of
the atom!
• The nucleus is the dense,
positively charged center of
the atom
• He came up with the Nuclear
Atomic Model
Nuclear Atomic Model
Nucleus
Electron
• Years later, Rutherford
discovered the proton
• proton = a positively charged
particle inside the nucleus
+
nucleus
proton
James Chadwick
• worked with Rutherford
• discovered the neutron – a
particle in the nucleus with the
SAME MASS as a proton, but
with NO charge (it’s neutral)!
Modern Atomic Structure
• spherically shaped
• most of atom’s mass is in the
nucleus (99.7%)
• nucleus surrounded by
negative electrons
• Atoms have no charge (they are
electrically neutral) because the
number of protons is equal to
the number of electrons
-
-
+
+
+
-
3 protons (+)
3 electrons (-)
particle
relative
mass
location
charge
–
in space
around
nucleus
–
9.11 x 10
proton
p+
inside
nucleus
+
1.673 x 10
– 24
1
neutron
n0
inside
nucleus
no
1.673 x 10
charge
– 24
1
electron
symbol
e
mass (g)
*Electron has the least mass
– 28
_1__
1840
You Made It!!!
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