History of the Atom

This set of flashcards covers the major milestones and theories in the history of atomic structure, including contributions from key scientists.

What is atomic theory?

Atomic theory is the idea that everything is made up of tiny particles that cannot be broken down further and are separated by empty space.

Who proposed the atomic theory and when?

Democritus proposed atomic theory around 500 BC.

What did John Dalton describe atoms as?

John Dalton described atoms as solid spheres.

What significant model did JJ Thomson propose?

JJ Thomson proposed the plum pudding model, suggesting that atoms contain negatively charged particles (electrons) within a positive charge.

What experiment did Ernest Rutherford conduct in 1909?

Ernest Rutherford fired positively charged alpha particles at a thin sheet of gold to test the plum pudding model.

What conclusion did Rutherford reach from his gold foil experiment?

Rutherford concluded that there is a compact nucleus containing all of the positive charge, and the negative charge exists in a cloud around it.

What flaw did Rutherford's model have?

Rutherford's model suggested a flaw where there was nothing preventing the electrons from collapsing into the nucleus.

Who proposed the solution to Rutherford's flaw and what was it?

Niels Bohr proposed that electrons orbit the nucleus in shells, preventing the atom from collapsing.

What particles did further experiments by Rutherford reveal to be in the nucleus?

Further experiments revealed that the nucleus contains positive charged particles known as protons.

Who discovered neutrons and when?

James Chadwick provided evidence for neutral particles known as neutrons in the nucleus.