Ernest Rutherford bombarded nitrogen atoms with
helium nuclei (alpha particles), and hydrogen
atoms (protons) were
formed as a result. From this, he concluded that
nitrogen nuclei contained protons.
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Rutherford's experiment for the discovery of the
Great question! Rutherford's experiment was
incredibly powerful due to its simplicity, use of
cheap materials, and the information he
uncovered. Rutherford's main focus was on
studying the nucleus through radioactive decay.
After the electron was discovered by Thomson in
1897 and after Rutherford's work on discovering
the existence of the nucleus 1911, it was known
that there must exist particles of positive charge
to balance the negatively charged electrons to
create electrically neutral atoms.
The series of experiments, performed by Rutherford
and his student James Chadwick, consisted of
changing one element into another by hitting atoms
with high energy alpha particles.
Specifically, they noticed that nitrogen, oxygen,
and aluminum, when hit with an alpha particle,
disintegrated and emitted a fast particle of
positive charge. Or said more specifically,
hydrogen nuclei were always emitted in the
process. In a dark room, they were able to observe
flashes of light when alpha particles hit the
target. Alpha particles, which were also
discovered by Rutherford, are spontaneously
emitted by radioactive materials such as uranium.
It was realized that the positive charge of any
nucleus could be accounted for by a whole
(integer) number of positively charged hydrogen
nuclei, which were named protons by Rutherford in
They immediately wondered what was left behind
on the target after this process occurred. The
conclusion was that the target captured the alpha
particle (2+ charge) and emitted a proton (1+
charge), resulting in the target having a nuclear
charge different than before. The target was now
an isotope of another element. In the case of a
nitrogen target, the nitrogen had a nuclear charge
of 8 instead of seven, making it an isotope of
oxygen (an isotope is an atom with the same
charge but a different atomic weight.) This
describes how the proton itself was discovered.
Many key experiments by Rutherford, his
students, and others occurred before this and led
to the understanding of the atom that is still the
accepted model today.
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