History of Atoms

Democritus' Atom

Indivisible and invisible particles theorized by Democritus around 460 B.C., referred to as 'atomos'.

Dalton's Atomic Theory

John Dalton's theory from around 1800 presenting atoms as indivisible solid spheres and introducing the Law of Definite Proportions and the Law of Multiple Proportions.

Thompson's Electron Discovery

J.J. Thompson's discovery of the electron through the cathode ray tube experiment, proposing the 'raisin bun' model of the atom around 1900.

Rutherford's Nucleus Discovery

Ernest Rutherford's 1911 Gold Foil Experiment leading to the discovery of the nucleus and the atom's composition of mostly empty space.

Maxwell's Electromagnetic Wave Theory

James Maxwell's mid-1800s description of light as an electromagnetic wave with continuous wavelengths forming a spectrum.

Photoelectric Effect

Heinrich Hertz's 1887 discovery where light with high frequency emitted electrons from a metal surface.

Planck's Quantum Theory

Max Planck's conclusion from blackbody experiments that energy is emitted in discrete quantities, represented by E = nhf.

Bohr's Quantum Model

Niels Bohr's 1913 quantum model of the atom based on electron wave properties, featuring stationary orbits with constant energy levels and light emission or absorption during energy transitions.

Bohr's Model Limitations

Bohr's model explains the first 20 elements of the periodic table, offers a 2D electron location representation, but lacks a complete quantum mechanical description.