#Atomic theory timeline project series#

1915 Arnold Sommerfeld develops a modified Bohr atomic model with elliptic orbits to explain relativistic fine structure.1914 Ernest Rutherford suggests that the positively charged atomic nucleus contains protons.1914 James Franck and Gustav Hertz observe atomic excitation.

#Atomic theory timeline project series#

1913 Johannes Stark demonstrates that strong electric fields will split the Balmer spectral line series of hydrogen.

1913 Robert Millikan measures the fundamental unit of electric charge.

1913 Niels Bohr presents his quantum model of the atom.

1913 Henry Moseley shows that nuclear charge is the real basis for numbering the elements.

1913 William Henry Bragg and William Lawrence Bragg work out the Bragg condition for strong X-ray reflection.

1912 Walter Friedrich and Paul Knipping diffract X-rays in zinc blende.

1912 Max von Laue suggests using crystal lattices to diffract X-rays.

1911 Ștefan Procopiu measures the magnetic dipole moment of the electron.

1908-1911 Jean Perrin proves the existence of atoms and molecules with experimental work to test Einstein's theoretical explanation of Brownian motion.

1911 Ernest Rutherford explains the Geiger–Marsden experiment by invoking a nuclear atom model and derives the Rutherford cross section.

1909 Ernest Rutherford and Thomas Royds demonstrate that alpha particles are doubly ionized helium atoms.1909 Hans Geiger and Ernest Marsden discover large angle deflections of alpha particles by thin metal foils.1906 Charles Barkla discovers that each element has a characteristic X-ray and that the degree of penetration of these X-rays is related to the atomic weight of the element.1905 Albert Einstein explains the photoelectric effect.1902 Philipp Lenard observes that maximum photoelectron energies are independent of illuminating intensity but depend on frequency.1900 Max Planck states his quantum hypothesis and blackbody radiation law.1900 Johannes Rydberg refines the expression for observed hydrogen line wavelengths.1900 Paul Villard discovers gamma-rays while studying uranium decay.1896 Wilhelm Conrad Röntgen discovers the X-rays while studying electrons in plasma scattering X-rays-that were considered as 'waves' of high-energy electromagnetic radiation- Arthur Compton will be able to demonstrate in 1922 the 'particle' aspect of electromagnetic radiation.1887 Heinrich Rudolf Hertz discovers the photoelectric effect that will play a very important role in the development of the quantum theory with Einstein's explanation of this effect in terms of quanta of light.1898 William Ramsay and Morris Travers discover neon, and negatively charged beta particles.1898 Marie and Pierre Curie discovered the existence of the radioactive elements radium and polonium in their research of pitchblende.1897 Emil Wiechert, Walter Kaufmann and J.J.1896 Pieter Zeeman studies the splitting of sodium D lines when sodium is held in a flame between strong magnetic poles.1896 Antoine Henri Becquerel discovers the radioactivity of uranium.1895 William Ramsay discovers terrestrial helium by spectroscopically analyzing gas produced by decaying uranium.1894 Lord Rayleigh and William Ramsay discover argon by spectroscopically analyzing the gas left over after nitrogen and oxygen are removed from air.1887 Heinrich Hertz discovers the photoelectric effect.

1885 Johann Balmer finds a mathematical expression for observed hydrogen line wavelengths.1873 Johannes van der Waals introduces the idea of weak attractive forces between molecules.1871 Dmitri Mendeleyev systematically examines the periodic table and predicts the existence of gallium, scandium, and germanium.1839 Alexandre Edmond Becquerel discovered the photovoltaic effect.1832 Michael Faraday states his laws of electrolysis.1811 Amedeo Avogadro claims that equal volumes of gases should contain equal numbers of molecules.1805 (approximate time) Thomas Young conducts the double-slit experiment with light.1803 John Dalton introduces atomic ideas into chemistry and states that matter is composed of atoms of different weights.1800 William Nicholson and Anthony Carlisle use electrolysis to separate water into hydrogen and oxygen.1781 Joseph Priestley creates water by igniting hydrogen and oxygen.1778 Carl Scheele and Antoine Lavoisier discover that air is composed mostly of nitrogen and oxygen.1766 Henry Cavendish discovers and studies hydrogen.430 BCE Democritus speculates about fundamental indivisible particles-calls them ' atoms'.6th - 2nd Century BCE Kanada (philosopher) proposes that anu is an indestructible particle of matter, an 'atom' anu is an abstraction and not observable.( Discuss) Proposed since November 2023.Ī timeline of atomic and subatomic physics. It has been suggested that Timeline of particle physics be merged into this article.