Uploaded by D Allen

History of the atom

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History of the atom
The time line shows how scientists’ ideas about atoms have changed. Scientists create theories based on
evidence they have, but these can be modified or new theories arise, as new evidence emerges
Demoncritus and Leucippus in 400BC
John Dalton in 1805
JJ Thompson in 1897
Ernest Rutherford and team
in 1909 - 1911
Greek scientist suggest that substances are made of
particles. Called particles ”atomos” – meaning indivisible
Propose the atomic theory and coins the word atom.
The atomic theory said that different elements have
different atoms.
Propose the “plum pudding model”,
the negatively charged electrons
were thought to be randomly stuck
in a sphere of positive charge,
somewhat like raisins in fruit cake.
Mostly empty
space containing
electrons
Tiny dense nucleus
containing protons
and neutrons
Niels Bohr in 1913
James Chadwick in 1932
In this model, most of the mass of
the atom is concentrated at the
centre or nucleus. Most of the
space taken up by electrons is
empty space. Rutherford called
this model the ‘nuclear model’
Suggest the presence of electron shells
or energy levels. Said that electrons
move around the nucleus in shells or
energy levels with most of the area
outside the nucleus is empty space.
Shows that neutrons exist.
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