Atomic Theory History Overview

Democritus

Speculated atoms as indivisible, invisible matter. Called "Atomos"

Dalton

Introduced Law of Definite Proportions & Law of Multiple Proportions.

J.J. Thompson

Discovered electrons with cathode ray tube.

Rutherford

Discovered nucleus & atom's empty space with Gold Foil Experiment.

Maxwell

Described light as electromagnetic wave with continuous wavelengths.

Hertz

Discovered photoelectric effect.

Planck

Studied blackbody radiation, introduced energy quantization.

Planck's Equation

E = nhf; energy quantization formula.

Einstein

Explained photoelectric effect with photons & quanta.

Bohr

Developed quantum model of atom, introduced stationary orbits.

Bohr's Postulates

Electrons can change their energy level

de Broglie

Proposed wave-particle duality for electrons.

Wave-particle duality

Concept where particles exhibit wave-like behavior.

Heisenberg

Formulated Uncertainty Principle in quantum mechanics.

Uncertainty Principle

States impossibility of knowing both position and speed of a particle.

Schroedinger

Developed the Wave Equation to describe electron behavior.

Wave Equation

Formula to describe electron wave-like behavior.

Law of Definite Proportions

Atoms of the same element have the same mass; mass ratios in compounds are consistent.

Law of Multiple Proportions

Atoms combine in whole number ratios; no fractional combinations.

Billiard Ball Model

Early atomic model depicting atoms as indivisible solid spheres.

Gold Foil Experiment

Rutherford's experiment leading to the discovery of the atomic nucleus.

Rutherford's Hypothesis

Expected alpha particles to break through gold foil with minor deflections.

Hertz's Experiment

Shining light on a metal surface to observe electron emission.

Planck's Study

Investigated blackbody radiation, showing light intensity peaked and dropped.