History of the Atomic Model

Aristotle

400

Aristotle did not belive in the Atomic Theory. Instead thought that everything in the world was made up of two of four elements, fire, water, air, or earth in 400 B.C.

History of the Atomic Model

Period: 400 to Dec 7, 1932

Democritus

460

Democritus Created the first Atomic Model. In 460 B.C, Democritus theorized that all matter is made of indivisible particles. This theory was based on logical reasoning. Demortitus did not conduct any experiments.

John Dalton

Dec 31, 1808

Dalton linked elements to atoms. He cobined two theories, the law of conservation of mass and the law of defenite proprortions, to form the first atomic theory. Dalton claimed that all atoms were made of tiny indivisible and indestructable particles called atoms. He also thought that all atoms of the same element were identical.

JJ Thomson

Dec 31, 1897

Thomson went a bit fartger than Dalton had and proved that atoms were made up of smaller paricles that contain a charge. He performed and experiment involving sending electricity through a cathoderay tube and the tube glowed. This proved the small cathoderay particles must have had a negative charge because they bent towards the positive charge. He then proposed that all atoms contain electrons. Thomsn proposed a different model than that of Dalton's, called the Plum Pudding Model.

Hantaro Nagaoka

Dec 31, 1904

Hantaro Nagaoka was the first scientist to propose that the atomic theory was not based on physics. He exclaimed that the atomic model was based on the planet Saturn's rings.

Ernest Marsden

Dec 31, 1909

Marsden used Ernest Rutherfor's gold foil experiment and noticed that some of the particles went through the foil, whie others bounced off. This told him that there was a positive charge in the nucleus in all atoms.

Ernest Rutherford

Dec 31, 1911

Ernest Rutherford performed the gold foil experiment and came to the conclusions that there was a very dense, positively charged center-piece in the middle of an atom. He named the middle of each atom, the nucleus. His model was called the Nuclear Model but this model was rejected by the community.

Neils Bohr

Dec 31, 1913

Neils Bohr agreed that electrons orbited the nucleus like it was the sun but, he believed the electrons moved in orbits and not just randomly around the nuclus aat different energy levels. Bohr also believed electrons could move from one energy level to the next.

Henry Moseley

Dec 31, 1914

Using X-ray tubes, Moseley determined the charges of the niclei of most atoms and he explained that the atomic number of an atom is equal to the number of protons are in an atom.

Louis De Broglie

Dec 31, 1923

De Brogile proprosed that the moving electron particles had some properties that of a wave. A few years later, experiments proved his theory.

Erwin Schrodinger

Dec 31, 1926

Schrodinger came up with an equation describing energy, and position of electrons in an atom. After the solutions to his equations were proven correct, he created a new field of math.

James Chadwick

Dec 31, 1932

Chadwick confirmed JJ Thomson's idea of neutrons with his "modified" Nuclear Model, but is also called the Electron Cloud Model. Chadwick understood that electrons are found in an electron cloud that is found outside of the nucleus.

History of the Atomic Model

Period: Nov 1, 2013 to Dec 31, 2013