Atomic Theory Timeline

Democritus

400

Democritus came up with the theory that everything is composed of tiny units of matter called atoms. He also stated atoms are industrucable and between atoms there is empty space. The offical date of when he discovered this theory is currently unknown.

Antoine Lavoisier

Mar 26, 1772

Antoine iis known for identifying Oxygen and Hydrogen atoms. He also identified their part in combustion.

Daltons Atomic Theory

Mar 28, 1800

The Atomic Theory;

1. Elements are made of extremely small particles called atoms. 2. Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties.
   
2. Atoms cannot be subdivided, created, or destroyed.
3. Atoms of different elements combine in simple whole-number ratios to form chemical compounds
4. In chemical reactions, atoms are combined, separated, or rearranged.

John Dalton

Mar 28, 1803

John proposed atomic theory, which states that atoms cannot be made or destroyed.

Dmitri Mendeleev

Mar 28, 1834

Dmitri created his own version of the periodic table using properties of elements to improve the table.

Robert Millikan

Mar 28, 1868

Robert discovered the electron is negatively charged and has an electric charge.

Niels Bohr

Mar 28, 1885

Bohr made a model of the atom that showed a nucleus at the center of the atom with electrons orbiting it.

Erwin Schrodinger

Oct 1, 1887

Erwin helped develop the quantum theory of mechanics. He came up with a different idea of wave functions and wave mechanics. He also came up wtih the quantum mechanical model which shows that matter is on waves of energy.

Henry Mosely

Nov 23, 1887

Henry justified all the atomic numbers on the periodic table and he proved that the nucleus contains positive charges.

James Chadwick

Mar 28, 1891

James used gamma ray radiations to prove that there are uncharged particles within the atom called neutrons.

JJ Thomson

Apr 30, 1897

JJ discovered the electron through an experiement of his called "Cathode Ray Tube." A glass tube with a high voltage charge which then emits electrons to the side of the glass with positively charged patricles.

Plum Pudding Atomic Model

Mar 28, 1904

This model shows there is no nucleus within the atom but instead floating electrons within a cloud and the cloud represents the pudding and the electrons as the plums.

Gold foil experiment

Mar 27, 1909

This experiment was conducted to prove the structure of the atom. A particle emitter was shot at gold foil and some of the atoms went through the foil while some bounced back. The atoms were shown on a detecting screen surrounding the foil.

Ernest Rutherford

Oct 1, 1911

Ernest Rutherford came up with an updated model of what he believed was how an atom looked. This model consists mainly of space but it shows the atom has a necleus which is the center of the atom and positive charges within the atom.

Electron Cloud

Mar 28, 1925

The electron cloud desribes where electrons are as they rotate around the mucleus of the atom. The electron cloud model states that electrons don't rotate around the nucleus of the atom.