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John Dalton
He was born in 1776. He described atoms as tiny balls of material. He said the atoms of a particular element are all identical.
He used small wooden balls to model atoms and showed how they could combine to produce compounds. -
JJ Thomson
In 1897 at Cambrige University he discovered "Cathode rays"
He discovered the electron.
Thomson came up with a model for atoms based in his discovery. He said that because atoms themselves had no charge there must be a positive charge inside the atoms to cancel out the charge on the negative electrons. He said that atoms were solid lumps of positively charge material with the electrons scattered through it like the fruit in a plum pudding.
"Plum Pudding" model. -
Ernest Rutherford
In 1911 Ernest Rutherford carried out an experiment that proved that atoms were not solid lumps of material as thought by Thomson but were in fact mostly empty space with a very small solid centre called the nucleus.
He came up with a new model which had a solid, positively charge centre and the negative electrons in "orbits" around it. -
Niels Bohr
In 1913, not long after Ruherford's discovery a Danish Physicist called Niels Bohr carried out some measurements on the energy emitted and absorbed by atoms and came up with the theory that the electrons inhabited fixed orbits or shells. This became known as the Bohr model of the atom and is the one we use today.
The Bohr model. A central, positive nucleus and the electrons in fixed orbits or shells around it. Larger atoms have more shells. -
James Chadwick
The Neutron was finally identified by him working in Cambridge. He realised that an unusual radiation that had been observed in some experiments was in fact a neutral, sub-atomic particle.
