Atomic Models
Timeline in Science
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
John Dalton (1808)

Davy isolates
– Sodium
– Calcium
– Barium

Daltons model
– Matter is made of atoms
– Element own type of atom
– Combine in fixed ratios
J.J Thompson (1897)

Subatomic particles
– Electron
– Negative charge

Thompson’s pudding
– Positive substance
– Negative electrons
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
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
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