Atomic Theory Research

Democritus

370

Greece
Idea-Matter is made of small indivisible particles which have different form, position, and arrangement.
Contribution of the understanding of atom- All matter is made of atoms that have different positions and arrangements.

Newton

Jan 1, 1704

England
Idea-The universe is a mechanical universe with small solid masses in constant motion.
Contribtuin to the understanding of atoms-An atom is a solid mass that is able to move.

Dalton

Jan 1, 1803

England
Idea- Spherical atoms have measureable properties of mass
Contribution to the understanding of atom- Atoms have a measurable mass.

G.J Stoney

Jan 1, 1894

Idea-Proposed that electricity was made of discrete negative particles, called electrons.
Contribution to the understanding of atom- Electrons have a negative charge.

J.J Thomson

Jan 1, 1897

England
Experiment- Discovered the electron and used cathode ray tubes to determine the charge to mass ratio of an electron to be 1.759 x 108 coulombs/ gram. He also found canal rays were associated with a proton.
Contirbution to the understanding of atom- Electrons have a charge to mass ratio of 1.759 x 108 coulombs/ gram.

Planck

Jan 1, 1900

Germany
experiment: Used quanta, discrete units of energy to explain glowing hot matter.

Nagaoka

Jan 1, 1903

Japan
Idea:There are flat rings of electrons revolving around a positively charged particle.
Contribution to the understanding of atom-Electrons revolve around the nucleus in rings.

Millikan

Jan 1, 1909

U.S.A
Idea-Determined the charge and the mass of an electron to be 1.602 x 10-19 C and 9.11 x 10-28 g respectively.
Contribution to the understanding of atom-The mass and charge of electrons

E. Rutherford

Jan 1, 1911

England
Idea-Determined that the nucleus is a small, dense, positively charged part of the atom.
Contribution to the understanding of atom- The nucleus is positively charged and therefore must hold the protons.

H.G.J. Moseley

Jan 1, 1914

England
Idea-Stated that the atomic number is equal to the number of protons in the nucleus.
Contribution to the understanding of atom-The atomic number is that number of protons in an atom

Bohr

Jan 1, 1922

Experiment- Created a model of successful orbital electron shells.
Contribution to the understanding of atom-Electrons orbit the nucleus in shells.

James Chadwick

Jan 1, 1932

England
Experiment- Discovered the neutron by using alpha particles.
Contribution of the understanding of atom- There is a subatomic particle called the neutron.