Atomic Timeline

Democritus

400 BCE

Democritus taught that there were substances called atoms and that these atoms made up material things.

Plato

375 BCE

Plato theorized that these solid forms of matter are composed of indivisible elements shaped like triangles.

Solar System Model

330 BCE

The Solar System Model was first proposed by plato that the planets followed perfect circular orbits around the Earth. Later, Heraclides developed the first Solar System model, placing the planets in order from the Earth it was is now called the geocentric solar system model.

The Alchemists

500

The Alchemists believed that all metals were formed from two principles, Mercury and sulfur.

Robert Boyle

1650

Robert Boyle believed that all matter was made of tiny particles that he called corpuscles

Antone Lavoisier

1772

Antone Lavoisier was a French chemist who through a series of experiments found that the total mass of products and reactions in a chemical reaction it is always the same

Billiard Ball Model

1800

Billiard Ball Model came from Dalton's Model of an Atom. It is often referred to as a billiard ball because he defined an atom to be a ball-like structure.

John Dalton

1803

John Dalton's theory suggested that all mater was comprised of invisible and indestructible atoms with distinct masses and properties

Amedeo Avogadro

1811

Amedeo Avogadro made Avogadro's law that states that equal volumes of gases under the same conditions of temperature and pressure will contain equal numbers of molecules.

Dmitri Mendeleev

1869

Dmitri Mendeleev devised that the periodic classification of the chemical elements

Robert Millikan

1890

Robert Millikan's major success was the accurate determination of the charge carried by an electron using the elegant "falling drop method". A fact about Robert Millikan is that he succeeded in precisely determining the magnitude of the electron's charge.

Pierre and Marie Curie

1898

Pierre and Marie Curie discovered the strongly radioactive elements polonium and radium.

JJ thompson

1900

JJ Thomason's experiments with cathode ray tubes showed that all atoms contain tiny negatively charged subatomic particles or electrons.

Plum Pudding Model

1904

Plum Pudding Model was developed by Thomson. In Thomson's plum pudding model of the atom, the electrons were embedded in a uniform sphere of positive charge, like blueberries stuck into a muffin.

Albert Einstein

1905

Albert Einstein mathematically predicted the size of both atoms and molecules.

Neils Bohr

1913

Neils Bohr developed the Bohr model of the atom, in which he proposed that energy levels of electrons are discrete

Henry G.J. Mosely

1913

Henry G.J. Mosely's law states that the square root of the frequency of the X-Ray emitted by an atom is proportional to its atomic number.

Ernest Rutherford

1917

Ernest Rutherford's atomic model was also known as the "Rutherford nuclear atom" and the "Rutherford Planetary Model"

Werner Heisenberg

1925

Werner Heisenberg formulated a type of quantum mechanics based on matrices.

Erwin Schrödinger

1926

Erwin Schrödinger formulated a wave equation that accurately calculated the energy levels of electrons in atoms.

Electron Cloud Model

1926

Electron Cloud Model Is a model that is showing a function that can be used to calculate the probability of finding any electron of an atom in any specific region around the atom's nucleus. The model was made by Erwin Schrödinger and Werner Heisenberg.

James Chadwick

1932

James Chadwick in may of 1932 announced that the core also contained a uncharged particle which he called the neutron