The science animation explains
the following in a story like manner using in-depth explanation,
the discovery of nucleus.
Lord Rutherford while studying the nature of the
Curie's radiation discovered that the radioactive elements
emit three types of radiations with different penetrating
power namely alpha (least penetrated), beta
(moderately penetrating) and Gamma (highly penetrating).
When these radiations were subjected to electric fields,
alpha rays were found to be positively charged particles
while beta rays were found as negatively charged light particles.
Gamma rays were found to be neutral in nature.
While studying the properties of these radiations, Rutherford
noticed that the beam of alpha rays when were made to fall
on a photographic plate by passing it through air, the edges
of the slit became diffused and widened. He concluded that
the alpha rays were scattered by air molecules.
To get a clearer evidence about the scattering he along
with his co-workers Geiger and Marsden built an apparatus
to bombard alpha particles on thin metallic foils. The metallic
foil he selected for his experiment was a very thin gold
Now if the atoms were actually arranged according to Thomson,
then the alpha particles would go undeflected. But during
experimentation it was found that though most of the alpha
particles went right through the thin foil, a few alpha
particles rebounded almost directly backwards. These
large angle deflections were not consistent with Thomson's
From the above observations he concluded that large
scattering angles could only occur if most of the mass
of the atom, and all of its positive charge reside in a
very small, extremely dense region called the atomic nucleus.
Thus Rutherford established a new model of the atom that
was similar to the structure of planets in orbit around
the sun. Rutherford's model consisted of a dense positive
core at the center of the atom with electrons orbiting around
it. This is called as Planetary Model of the atom.
Though Rutherford was successful enough to explain the rearrangement
of the charged particles within the atom, his model faced
some serious problems.