The Development of the Atomic Theory

Democritus

400 BCE

Democritus' atomic theory implied that all matter is made of small indestructible units known as "atoms". By this logic, there are as many elements as there are things in the world.

Christiaan Huygens

1678

Christiaan Huygens, believed that light was made up of waves vibrating up and down perpendicular to the direction of the light travels, and therefore formulated a way of visualising wave propagation

Isaac Newton

1704

Proposed a "mechanical" universe with small solid masses in motion. In short, he believed that there were little tiny pieces of mass that were 'swimming' everywhere.

John Dalton

1803

Dalton, like Democritus, proposed that all matter was composed of atoms, indivisible and indestructible units. While all atoms of an element were identical, different elements had atoms that varied in size and mass. He also proposed that compounds were formed by a combinition of these differing elements.

Gustav Kirchhoff

1862

Theorized that black-body radiation (An object that absorbs all radiation falling on it, at all wavelengths, is called a black body.) emitted by heated objects, spectroscopy, and electrical circuits.

James Maxwell

1873

Maxwell proposed the theory of electromagnetism and made the connection between light and electromagnetic waves. He discovered how electrons also have wave like properties.

Heinrich Hertz

1887

German physicist who first conclusively proved the existence of the electromagnetic waves theorized by James Clerk Maxwell's electromagnetic theory of light.

J.J Thompson

1897

Discovers the electron by experimenting with cathode rays. His finding suggested that the rays were negative.
He is also responsible for the “plum pudding” model, which suggested that that an atom had stationary protons situated in the middle of the atom, with negatively charged electrons scattered throughout the atom.
Rutherford

Max Planck

1900

The originator of the quantum theory, the minimum amount of any physical entity (physical property) involved in an interaction.

Erwin Schrodinger

1900

He treated the electron as a wave, which gave rise to the Quantum Mechanical Model.

Albert Einstein

1905

Responsible for the theory of relativity (the laws of physics are the same for all non-accelerating observers), which laid the basis for the release of atomic energy. He also showed that the speed of light within a vacuum is the same no matter the speed at which an observer travels.

Ruhterford

1911

Rutherford overturned Thompsons model with his infamous gold foil experiment in which he demonstrated the the atom has a small and heavy nucleaus.

Bohr

1913

Bohr discovered that atoms travel in orbits around the nucleus. He also discovered that the amount of electrons in the valence shell changes the properties of an element.

Arnold Summer Field

1915

Boldly employed elliptical orbits to extend the Bohr theory and successfully explain this line "splitting"

Wolfgang Pauli

1925

Suggested that each electron spin on its axis. He also theorized that electrons can move in one two ways, using the analogy of a top that can spin both clockwise and counterclockwise.

Bohr/Heisenberg

1925

Developments in quantum mechanics led to its becoming the standard formulation for atomic physics. In this summer, Bohr and Heisenberg published results that closed the old quantum theory.