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Greeks proposed that all matter was composed of four fundamental substances: fire, water, earth, and air. Based on intuition Not based on experimental evidence
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Each element is made up of tiny particles called atoms.
The atoms of a given element are identical.
Chemical compounds are formed when atoms combine with each other.
Chemical reactions involve reorganization of the atoms. The atoms themselves are not changed in a chemical reaction. -
Discovered the electron.
All atoms have electrons.
Developed the plum pudding model -
Metal foil experiment
Atom has a center of concentrated positive charge
Center contains most of the mass of the atom
Center called the nucleus
Nuclear Atom
Electrons move around the nucleus at a distance relative to the nuclear radius -
Developed the quantum model for the hydrogen atom Electron in a hydrogen atom moves around the nucleus only in certain allowed circular orbits