1. Atomic Theory Timeline
Development of our understanding
of the atom

2. 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

3. 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

4. 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”

5. 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

6. What we believe now Orbital proposed by Schrödinger
Describes most likely where electrons were
Quantum mechanics new theory
“Electron Cloud” model