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Atomic Theory Timeline
Development of our understanding
of the atom
Early Models Democritus was first to suggest atom in 4th
century B.C. Dalton’s model was the “Billiard Ball”
Atomic Theory Matter is composed of atoms Atoms are indivisible Atoms of a given element have same size, mass and
chem props and are different from those of another element
Different atoms combine in whole number ratios to form compounds and are separated, combined and rearranged in chem reactions
Conservation of Mass
Early Models
Thomson used the Cathode Ray – determined atoms were made of particles Negative charges in atom “Plum Pudding” model
Millikan used oil drop experiment Found mass and charge of an electron
Important discoveries
Rutherford experimented with Gold Foil Found nucleus Discovered its positive charge and tiny size Electrons moving around the nucleus Came up with “Nuclear Model”
Moving Forward…
Bohr said electrons move in orbits Found in energy levels Explains bright-line spectrum Called “Planetary Model” But Bohr knew that it was flawed
What we believe now
Orbital proposed by Schrödinger Describes most likely where electrons were
Quantum mechanics new theory “Electron Cloud” model