Developement of Ideas About the Atom

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'.

Life of John Dalton

Life of J.J. Thompson

Life of Hans Geiger

Life of Ernest Marsden

Life of Ernest Rutherford

Life of Niels Bohr

Life of James Chadwick