1. Atomic Models Timeline in Science

2. Empedocle (420 B.C)  The word Atom was introduced by Leucippe and it means Indivisible  Qualities –Indivisible due to size –Solid (no void) –Perfect therefore eternal –Surrounded by empty space –Infinite number of shapes Earth Water Air Fire

3. John Dalton (1808)  Davy isolates –Sodium –Calcium –Barium  Daltons model –Matter is made of atoms –Element own type of atom –Combine in fixed ratios

4. J.J Thompson (1897)  Subatomic particles –Electron –Negative charge  Thompson’s pudding –Positive substance –Negative electrons

5. Ernest Rutherford (1911)  Subatomic particles –Nucleons  Protons positively charges  Neutrons no charge (Chadwick 1932) –Majority of the mass  Planetary Model –Electron moves around the nucleus like planets around the sun –Mostly empty space –Indivisible

6. Niels Bohr (1913)  Atomic Stability –No crashes  Electron emits light  Loses energy  Orbit Model –Positions Quantified –Only certain orbits are allowed –Jump between orbits emits (or absorbs) light

7. Electron Cloud Model (1924)  Why limited to given orbital? –Electron moves in clouds  Erwin Schrödinger and Louis de Broglie –Can’t know the exact location –Probabilistic model