Chapter 1 The history of the atom

Date Name Theory Representation

442 BC 4th century

BC

Democritus

Aristotle

Invisible particles called “atomos” 5 elements: earth, wind, water, fire,

and aether ∅

1805 Dalton Billiard Ball: atoms are solid spheres

1897 Thomson Plum Pudding model: electrons are

embedded in a cloud of positive charge

1911 Rutherford

Planetary model: atoms consist of a small dense center fill with positive charges (the nucleus), electrons are

orbiting around the nucleus

1914 Bohr Energy Level model: electrons can

only have certain fixed energies; they can jump from a level to another one.

1926 Schrödinger

Electron cloud: Electrons don’t move in orbits (or in a set path). He stated that they move in waves, and they have no exact location.

1932 Chadwick Discovered the neutron