Past Theories

By Todd Eichel

Many theories have been proposed to explain the nature of our universe. Before the current theory was accepted, scientists had many different views.

The Greek Model
- Democtritus (450 B.C.)
- Proposed that matter couldn't be divided into smaller and smaller pieces forever. Eventually, the smallest piece of matter would not be divisible anymore. He called these indivisible pieces "atomos"
Aristotle (around 450 B.C.)
- Scoffed at Democritus
- Proposed that everything is made up of four elements
  - Air
  - Water
  - Earth
  - Fire
- Led to Alchemy in the middle ages.
The Dalton Model
- John Dalton (1803)
- All mater composed of tiny particles called atoms.
- Atoms cannot be created, destroyed, or subdivided.
- Atoms of the same element are identical in size, shape, and color.
- Atoms of different elements are different.
- Atoms combine in simple whole number ratios to form compounds.
- Chemical reactions are simply the separation, combination, or rearrangement of atoms.
The Thomson Model (also known as the Plum-Pudding Model)
- J.J. Thomson (1897)
- Proposed atom as a mass of positively charged material with negatively charged electrons scattered throughout.
The Rutherford Model
- Ernest Rutherford
- Proposed atom as mostly empty space, having a positively charged nucleus and electrons scattered around the edge.
The Bohr Model (also known as the Planetary Model)
- Neils Bohr (1913)
- Stated that electrons move in definite orbits around the nucleus, like planets orbiting a star.
- Proposed that each electron moves at a specific energy level.
The Wave Model
- Based on wave mechanics
- Proposed that electrons have no definite path in an atom.
- Stated that the probable location of an electron is based on how much energy it has.
- The more energy an electron has, the farther it is away from the nucleus.
- The small, positively charged nucleus is surrounded by a large space in which there are enough electrons to make the atom neutral.