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1
2
3
4
6
5
7
8
6
1954
CERN, the world’s largest
nuclear physics research center,
located in Switzerland, is founded
to study particle physics.
7
1968
Scientists provide the first
experimental evidence for subatomic
particles known as quarks.
5
1938
Lise Meitner, Otto Hahn,
and Fritz Straussman split
uranium atoms in a process they
called fission.
4
1932
James Chadwick proves
the existence of neutrons.
1
1897
Using cathode-ray tubes,
J.J. Thomson identifies the
electron and determines the ratio
of the mass of an electron to its
electric charge.
2
1911
With the gold foil experiment,
Ernest Rutherford determines
properties of the nucleus, including
charge, relative size, and density.
3
1913
Niels Bohr publishes a
theory of atomic structure relating
the electron arrangement in atoms
to atomic chemical properties.
8
2010–2013
The Large Hadron
Collider at CERN smashes
beams of protons at the highest
energy ever, allowing scientists
to find a particle consistent with
the predicted properties of the
Higgs boson.
Development
of
Modern
Atomic Theory
Current understanding of the properties and
behavior of atoms and subatomic particles is
based on the work of scientists worldwide
during the past two centuries.
Figure 13
Lesson 2 • Defining the Atom
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