Core theories

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Core theories

Atomic Theorists & Models

* claimed there are four elements: fire, air, earth and water.* first to theorize that matter can be broken down into simpler things

Aristotle and Empedocles

Democritus and Leucippus

they concluded that the atom was a tiny indestructible sphere like object, which everything is made of. First used the word "atomos"


*Joseph John Thomson made his major contribution to the atom in 1897.Thomson discovered the electron in a series of experiments designed to study the nature of electric discharge in a high-vacuum cathode-ray tube.Thomson interpreted the deflection of the rays by electrically charged plates and magnets as evidence of “bodies much smaller than atoms", or electrons.*concluded that in the atom, there are smaller particles with electrical charges called electrons.


*the atom as a tiny, dense, positively charged core called a nucleus, in which nearly all the mass is concentrated, around which the light, negative constituents, called electrons, circulate at some distance, much like planets revolving around the Sun.


1) All matter ismade of atoms. Atoms are indivisible and indestructible.2) All atoms of a given element are identical in mass and properties3) Compounds are formed by a combination of two or more different kinds of atoms.4) A chemical reaction is a rearrangement of atoms.


Oil was sprayed out of an atomizer. The small oil drops would pick up some unknown number of electrons due to friction between the oil and the nozzle. These oil drops were sprayed between two oppositely charged parallel plates. The weight of an oil drop could be calculated by using the terminal velocity of the freely falling oil drop and the formula for terminal velocity of a sphere. Once the weight was determined, the voltage across the plates could be adjusted until the upward electric force exactly cancelled out the weight of the oil drop. When the exact balance was reached, the oil drop could remain suspended between the plates.determined electrons have negative charge.


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