Atomic Model Cut and Paste Note page
THE HISTORY OF THE
ATOMIC MODEL
John Dalton – Early 19th century (1808)
James Chadwick – 1932
Niels Bohr – Early 20th Century (1913)
J.J. Thomson – 1897
Ernest Rutherford -1906/1911
Electron Cloud Model – 1932 to present
He was a scientist/school teacher.
He said atoms were the smallest
particles of matter. He said atoms
could not be destroyed or divided.
He thought atoms were hard spheres
that were the same throughout.
His model was similar to a marble.
He discovered the nucleus of the
atom. He also determined that
the nucleus was small and dense.
It made up most of the mass of
an atom. He proposed that most
of the atom was made up of empty
space. (He experimented with alpha
particles and gold foil).
This 20th century scientist worked
on a theory to explain how electrons
are arranged in the atom. He proposed
the idea that energy levels or shells
housed the electrons which he thought
moved around the nucleus much the
way a planet orbits the sun.
He worked with Ernest Rutherford
and was credited for discovering the
neutron. The neutron was proposed
when Rutherford’s model could not
explain why the nucleus was 2 times
the mass of the number of protons.
This scientist discovered the electron.
His model of the atom was a sphere of
positive charge with negatively charged
particles spread evenly throughout. His
model was likened to a “raisin bun”.
This is the most current model of the atom.
It states that electrons are in constant motion
around the nucleus. This motion is unpredictable
and can’t be described by an orbit. The new
model simply defines a region (the electron cloud)
where the electrons are most likely to be found.