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# Democritus

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

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

England
Idea- Spherical atoms have measureable properties of mass
Contribution to the understanding of atom- Atoms have a measurable mass.
• # G.J Stoney

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

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

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

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

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

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

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

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