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400 BCE
Democritus
According to Democritus atoms were miniscule quantities of matter. Democritus hypothesized that atoms cannot be destroyed, differ in size, shape and temperature, are always moving, and are invisible. He believed that there are an infinite number of atoms. -
384 BCE
Aristotle
Aristotle had believed that everything in the world is made of four elements, these are: fire, earth, water, and air. -
Dalton
Elements are made up of atoms, all the atoms in an element are identical but are different then those of any other element -
Cathode-ray tube experiment
In a cathode-ray tube, fast moving electrons excite gas making it glow between the electrons. He also found that cathode-rays can be deflected by an amplified electric field -
Thomson
Negative electrons are embedded in a sea of positive charge -
Gold foil Experiment
Rutherford, proved that atoms had a center(nucleus) -
Oil drop experiment
Millikan's, oil drop experiments allowed for the determination of the charge and mass of an electron. -
Rutherford
Positive charge is located within a central nucleus -
Bohr
Based on quantum theory that energy is transferred only in certain well defined quantities. Electrons should move around the nucleus but only in prescribed orbits. When jumping from one orbit to another with lower energy, a light quantum is emitted. -
Electron Cloud Model
Electrons appear and disappear at random in clouds, 2 electrons per cloud 1st and 2nd time around are in a circle and the 3rd is crazy