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420 BCE
Democritus
Things are made of atoms
420 BC
First Atom
held that everything is composed of "atoms," which are physically, Observed that if you manipulated the same items the same way, you'd get the same results -
Dalton
1800s
Atoms of the same element have the same properties
Did Not create a model
Law of Conservation of Mass. Found out that the atoms of the same element have the same mass by exploring mass ratios -
JJ Thomson Electrons and Plum Pudding Model
England 1890
Plum Pudding Model
States that atoms/ matter contained an even distribution of positive and negative charge
There exist particles that are smaller than an atom
Cathode Ray Tube -
Robert Millikan Charge and size of an electron
America 1909
Charge and size of an Electron
Subatomic particle that Thomson found is actually negative
Use the effect that two charged plates had on charged oil to measure how how an electron weights -
Ernest Rutherford Electrons orbit a dense nucleus
England 1911
The nucleus of an atom
Most of an atom is empty space that surrounds a dense nucleus
We finally have structure to the atom
Fired alpha particles through gold foil -
Niels Bohr Electrons orbit the nucleus in clearly defined orbits
Denmark 1919
A positively charged nucleus is orbited by negatively charged electrons
Electrons in energy shell
We now have a general location of where different subatomic particles are
Used the way that different atoms release light when they are excited to show that different atoms absorb -
Modern Atomic Theory
Modern Atom. Culmination of all previous scientists.
Electron cloud
We now know that Electrons do not exist in clean orbits, but instead in an electron cloud (Location where electrons are most likely to be found)
Comes from all previous experiments/ ideas