Atomic theory timeline

Plato

440 BCE

Plato's theory of forms asserts that the physical world is not really the real world. Instead, ultimate reality exists beyond our physical world.

Democritus

400 BCE

Democritus was a central figure in the development of the atomic theory of the universe he theorized that all materials bodies are made up of indivisibility small atoms.

Robert Boyle

1640

Robert Boyle stated that if the volume of a gas is decreased the pressure increases proportionally.

Antone Lavoisier

1789

Found the total mass of products and reactants in a chemical reaction is always the same. Led to the law of conservation of mass.

Billiard ball Model

1800

Because Dalton thought atoms were the smallest particles of matter, he envisioned them as solid, hard spheres, like billiard balls, so he used wooden balls to model them. Dalton added these so the model atoms could be joined together with hooks and used to model compounds.

The Alchemists

1803

By breaking the 4 basic elements of its period. By laying down the foundation of the modern-day periodic table of the elements.

John Dalton

1805

John Daltons Atomic theory proposed that all matter was composed of atoms, invisible and indestructible building blocks.

Dmitri Mendeleev

1869

Dmitri Mendeleev found that when all the known chemical elements were arranged in order of increasing atomic weight. the resulting table displayed a reoccurring pattern.

Robert Millikan

1890

Discovered that there is a fundamental electric charge the charge of a electron.

Pierre and Marie Curie

1898

Pierre and Marie Curie discovered the strongly radioactive elements polonium and radium which occur naturally in uranium minerals.

Neils Bohr

1903

Neils Bohr proposed a theory for the hydrogen atom based on quantum theory that some physical quantities only take discrete values.

Plum pudding model

1904

JJ Thomsons proposed the plum pudding model of the atom, which had negatively charged electrons embedded within a positively charged "soup."

Albert Einstein

1905

Albert Einstein mathematically proved the existence of atoms thus revolutionizing science.

Ernest Rutherford

1911

Ernest Rutherford found that the atom is mostly empty space, with nearly all of its mass concentrated in a tiny central nucleus.

Solar system model

1913

The Bohr or solar system model of the atom states that atoms consist of a nucleus with a number of electrons in orbits around that nucleus.

JJ Thompson

1914

JJ Tompson showed that all atoms contain tiny negatively charged subatomic particles or electrons.

Henry G.J. Mosley

1914

Henry G.J. Mosley concluded that the atomic number is the number of positive charges in the atomic nucleus.

Erwin Schrodinger

1926

Erwin Schrodinger showed that the quantization of the hydrogen atoms energy levels that appeared in Neils Bohr atomic model could be calculated from the Schroder equation.

Electron Cloud Model

1926

Erwin Schrödinger developed an Electron Cloud Model. It consisted of a dense nucleus surrounded by a cloud of electrons at various levels in orbitals.

James Chadwich

1932

James Chadwich discovered atoms consisted not only of protons and electrons but also neutrons.