Atomic Theory History

Democritus

The Greek philosopher who developed the idea of atomos, positing that the world is composed of tiny indivisible and indestructible particles.

John Dalton's Atomic Theory

The first atomic theory consisting of five principles, including that elements are made of indivisible atoms and that atoms combine in simple ratios to form compounds.

Electron

A negatively charged particle discovered by J.J. Thomson, which showed that atoms could be divided into smaller pieces.

Cathode Ray Tube

An experiment used by J.J. Thomson that demonstrated the existence of electrons through a stream produced at the negative electrode.

Robert Millikan

Scientist known for the oil drop experiment which determined the charge of electrons.

Ernest Rutherford

Discoverer of the nucleus and developer of the nuclear model of the atom, demonstrated by the gold foil experiment.

Gold Foil Experiment

An experiment conducted by Rutherford that showed most alpha particles passed through gold foil, indicating that atoms are mostly empty space.

Niels Bohr

Improved Rutherford's atomic model by introducing the concept of electrons in fixed orbits around the nucleus based on atomic emission spectra.

Energy Levels

Fixed orbits around the nucleus of an atom where electrons reside according to Niels Bohr's model.

Max Planck's Theory

Proposed that energy is quantized, and electrons must absorb whole packages of energy, relating to different frequencies of light.

Heisenberg Uncertainty Principle

The principle stating that one can determine either the velocity or position of an electron, but not both, as proposed by Werner Heisenberg.

Louise de Broglie

Suggested that only whole numbers of wavelengths are allowed in circular orbits of fixed radius, leading to the wave-particle duality of light.