atomic theory timeline

ancient greece's

500 BCE

Democritus was one of the first atomic theorists and had an extremely remarkable atomic theory that still relates to today's chemistry. Democritus believed that if you break a rock in half, both halves would be made of the same material. if you break the rock into smaller and smaller pieces eventually it becomes so small that it can't be divided and he called it an atomos which translates to indivisible.

Alchemists

384 BCE

Alchemy is the origin of chemistry and was created by the philosopher Aristotle, in which he believed that everything was made up of the four elements earth, air, fire, and water. alchemy was focused on goals like turning base metals into gold and discovering the elixir of life which would grant health, wealth, and immortality. although their work was not based on real science they were still able to discover a lot in the field of atomic theory.

John Dalton

1803

Daltons contributions to atomic theory is his theory that atoms are indivisible and the building blocks of matter. with the atoms being identical among the same element but different sizes and masses between different elements.

J.J.Thomson

1897

Thomson discovered the electron and created a new model of the atom that included the charged particles within the atom. he related the model to plum pudding, with the raisins being the electrons and the pudding containing a positive charge, failing to recognize positive charges as a particle.

Max Planck

1900

Plank discovered that the frequency of a wave is equal to the energy, as well as discovering was quantized.

Albert Einstein

1905

Einstein mathematically proved the existence of the atom which made it so that one could determine the size of an atom. he also discovered that liquids are made up of molecules that are in random motion and was able to find the rate they move at.

Ernest Rutherford

1911

Rutherford greatly improved the model of the atom. his model has a positively charged nucleus surrounded by empty space with very small electrons moving in that surrounding space of the nucleus. he also discovered the proton and hypothesized what was later discovered as the neutron.

Niels Bohr

1913

Bohr discovered that electrons in their orbitals can move up an orbital to a new energy level.

Louis de Broglie

1924

Louis de Broglie discovered that electrons don't only act like a particle but have a duality of also acting as a wave.

Wolfgang Pauli

1924

Pauli discovered the spin of electrons with either a spin-up or a spin down. along with this, he discovered that no two electrons can be in the same quantum state.

Werner Heisenberg

1925

Werner extended the work Schrodinger did by discovering how to find not only the position of the electron but the momentum of the electron as well.

Erwin Schrödinger

1926

Schrodinger used math to find the likely hood of the position that the elections are. his model is portrayed as electron clouds surrounding the nucleus.

James Chadwick

1932

Chadwick discovered the neutron which is a chargeless particle located in the nucleus. the stability of an atom is reliant on the balance of protons and neutrons which makes his discovery crucial in the discovery of nuclear fission.

Richard Bader

1991

Bader made large contributions in explaining the behavior of atoms in the molecule. This theory went against accepted theories because he believed that there are no orbitals which made it hard to publish.

Robert Le Roy

1994

Le Roy's theory explains the quantitative measurement and properties of the forces in molecular systems.