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400 BCE
Democritus
Atoms are "uncuttable".
"Atomos" means "not to be cut" which refers to the smallest piece of matter.
Atoms are made of a single material that is formed into different shapes and sizes. -
300 BCE
Aristotle
Matter has four properties: hot, cold, dry and wet.
All matter is made up of four elements: fire, air, water and earth. -
Period: 300 BCE to
Aristotle
Matter has four properties: hot, cold, dry and wet.
All matter is made up of four elements: fire, air, water and earth. -
Dalton
Atoms of the same elements are exactly alike.
Atoms of different elements are different. -
Thomson
There are small, negatively charged particles inside at atom called electrons.
This theory led to the "plum pudding" model, in which negative particles are stuck in a positively charged substance. -
Rutherford
There is a small, dense, positively charged nucleus.
Atoms contain mostly empty space.
Electrons are scattered around the nucleus at a distance. -
Bohr
Most of an atom's mass is in the nucleus.
Energy levels are located certain distances from the nucleus.
Electrons travel in paths called energy levels. -
Modern Cloud Theory
Electrons are found in electrons, not in paths.
Electrons move around the nucleus billions of times in a second.
Electrons' locations depend upon how much energy they have.
