Events
J.J. Thompson discovered tiny,
negatively charged, sub-atomic
particles in 1897 while studying
the conduction of electricity
through gases. This led him to
create the 'Plum Pudding' model.Dalton's work in the early 1800's
led to people accepting that
everything was made of atoms,
which he thought to be small,
indivisible particles.Geiger, Marsden, and Rutherford discovered the nucleus in 1911
following experiments to test the 'Plum Pudding' model. They
fired beams of alpha particles at a thin piece of gold foil,
expecting them to pass through. Many did, but some alpha
particles were deflected and others bounced straight back.
This, they discovered, was because the positively charged nucleus
was in the way.In 1913 , Bohr suggested that electrons
moved around the nucleus in stable
orbits known as 'shells' or 'energy levels'.In 1932, James Chadwick discovered chargeless neutrons.
This explained the mysterious mass that atoms had, that
could not be created by just electrons and protons,
and that did not interfere with the charge of the atom.At the time of Dalton's life, one of the best ideas about
atoms was Democritus'. Democritus lived in Greece
from around 460 BC to 370 BC. He was one of the
first people to think about atoms, and said that atoms
were the smallest particle in existence and that they
made up everything and were eternal and indestructible.
Atom comes from the Greek word 'atomos', meaning
'indestructible'.Periods
Life of John DaltonLife of J.J. ThompsonLife of Hans GeigerLife of Ernest MarsdenLife of Ernest RutherfordLife of Niels BohrLife of James Chadwick
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