History of the Atomic Model

Aristotle

200

Aristotle lived in the 500's B.C. He believed that there was no limit to how many times matter could be divided.

John Dalton

Sep 3, 1803

John Dalton's theory was that all atoms of the same element have the same mass, and atoms of different elements have different masses, that compounds contain atoms of more than one element, and in a particular compound atoms of different elements always combine in the same way. To come to his theory, Dalton measured masses of elements that combine when elements form.

J. J. Thomson

Jul 23, 1897

Thomson discovered subatomic particles and electrons by using an electric cord to positively charge a disk, and negatively charge another.

Hantaro Nagaoka

Aug 27, 1904

Nagaoka suggested a central nucleus and that electrons orbit around the atom

Ernest Rutherford

Oct 31, 1911

Ernest Rutherford stated that atoms have a nucleus that is dense and positively charged. He also said that electrons revolve around the nucleus. Rutherford was Marsden's teacher.

Ernest Marsden

Nov 1, 1911

Marsden aimed alpha particles at a sheet of gold to see how the gold atoms would affect the alpha particles. Marsden believed that the alpha particles would only be slightly deflected. Marsden discovered that the closer the particles came to the center of the gold atoms, the more deflected they became. This lead to the discovery of the nucleus. Ernest Marsden was Ernest Rutherford's student.

Niels Bohr

Nov 1, 1913

Discovered that each electron has a specific amount of energy. Energy levels- Possible energies an electron in an atom can have. An electron in an atom can move from one energy level to another when the atom gains or loses energy. To come to his conclusions, Bohr worked with Ernest Rutherford.

Louis de Broglie

Jan 1, 1924

Louis de Broglie is famous because he proposed the idea that particles move and have some waves like electrons. Broglie came to his conclusions by studying the atomic theories of the scientists of his time.

Erwin Schrodinger

Nov 1, 1926

Shrodinger created mathematical equations to describe the motion of electrons. He was able to come up with his equations by using Bohr's model and Broglie's concept.

Heisenberg

Oct 31, 1927

Described atoms by means of formula connected to the frequencies of spectral lines. Proposed Principle of Indeterminancy - you can not know both the position and velocity of a particle.

James Chadwick

Nov 1, 1932

James Chadwick was able to confirm the existence of nuetrons which have no charge. To prove this, he made an experiment

Enrico Fermi

Oct 31, 1942

Conducted the first controlled chain reaction releasing energy from the atoms nucleus.

Democritus

Jul 26, 2000

Domocritus lived in 500 B.C. He came up with the name atom through the work of discourse.