...Atomic Theory

The atom has had many different interpretations in the past, many of which have been proven wrong. Scientists over the years have corrected and worked on these ideas into a theory that we use today.


Four Element Theory  
-first theory of matter
-everything was made in part of water, wind, earth, fire.
(not a scientific theory because it could not be tested)


Democritus(300BC) 
-the first person to have interpreted the atom(atmos).
-Atoms were invisible
(not a testable theory, only a conceptual model)


Lavoisier(late 1700s)
-law of conservation of mass
-law of definite proportions
  water is always 11%(H) and 89%(O)


Proust(1799)
-if a compound is broken down into it's constituents, the products exist in the same ratio as in the compound.
-experimentally proved Lavoisier Laws


Dalton(early 1800s)
-atoms are solid, indestructible spheres (like Billiard balls)
-provides for different elements (these would be different spheres)
-based on the law of conservation of mass 


J.J Thomson(1850s)
-raisin Bun model
(solid, positive spheres, with negative particles embedded in them.)
-first atomic theory to have positive and negative charges
-demonstrated the existence of electrons using a cathode ray tube


Rutherford(1905)
-showed that atoms have a positive, dense center with electrons outside it.
-resulted in planetary model
-suggests atoms are mostly empty space


Bohr model(1920s)
-matter emits light when it is heated
-light travels  as photons
-the energy photons carry depends on their wavelengths