Rutherford’s Gold-Foil
Experiment
Radioactivity


Radioactivity had been
discovered recently, in 1895, by
Henri Becquerel, based on
Wilhelm Roentgen’s
“photograph” of his wife’s
hand’s bones.
Becquerel had put uranium
crystals into a drawer with
photographic plates, and they had
ended up “fogged.”
Further Research


Marie and Pierre Curie
isolated polonium and
radium.
They realized that
some elements emitted
energy, and some
emitted particles.
Rutherford and Radioactivity


Ernest Rutherford used
alpha particles to
investigate the gold atom in
1908.
He conducted a famous
experiment that proved that
atoms are not solid spheres
as proposed by Dalton, or
“plum-puddings,” as
Thompson said.
The Alpha Particles Experiment

In his experiment Rutherford used a very thin
sheet of gold as a target, and he shot a beam of
alpha particles at the gold.
–
alpha particles (-particles) are helium nuclei without
electrons, and are a form of radioactivity
Nearly all of the alpha particles passed through
the thin sheet of gold.
 Rutherford also noticed that a few particles were
deflected from their straight- line path, some by
90 degrees or more.

Conclusion
The beams were bouncing off the
positively charged core of the atoms.
 Rutherford originally called this a proton,
because it was positively charged.
 Later, it was renamed the nucleus. The
nucleus of the atom has almost all the mass
of the atom.
 Therefore, most of an atom is empty space.
