History of an Atom

Democritus was a Greek philosopher who was the first person to use the term atom (atomos: meaning indivisible).
He created a theory called theory of the universe:
-All matter consists of atoms, which are bits of matter too small to be seen.
-There is an empty space between atoms
-Atoms are comletely solid
-Atoms have no internal structure
-Each atom (of a different substance) is different in size, weight, and shape

John Dalton was the first to adopt Deocritus' theory into the first modern atomic model.
John Dalton's Atomic Model:
-All matter consists of tiny particles called atoms
-Elements are charcterized by the weight of their atoms
-Atoms are indestructable and unchangeable
-When elements react, it is their atoms that have combined to form new compounds

J.J Thomas was a physicist who is credited for discovering the eletron. He used his research on cathode ray tube technology in his discovery. He was an excellent physicist and thus did not stop whe he had fooud this negative charge. Through a series of clever experiments he was able to predicrt the mass of this charge.
-J.J Thomson found that this charge was 1000 times lighter than a hydrogen atom.

Using what he discovered, Thomson predicted what an atom should look like. These are the key pionts to Thomson's Atomic Model:
-It is known as th Plum Pudding model based on its design
-Each atom is a sphere with a positve charged 'Fluid'. This resembles the sticky jam part of a pudding.
-Corpuscles (later called electrons), are the negatively charged particles.
-He did not predict the movements of these electrons

Ernest Rutherford was not convinced about the model of the atom proposed by Thomson, he thus set up his now famous Gold Foil Experiment.
-He fired alpha particles (positively charged) at a gold foil
-He measured the deflection as the particles came out the other side.
-Most of the particles did not deflect at all, every now and then a particle would deflect all the way back
-He said there must be a positvely centre of the foil. He called this centre the nucleus

Rutherfords Atmic Model(aka the planetary model):
-The nucleus of the atom is a dense mass of positively charged particles
-Electrons orbit the nucleus
Its known as the planetary system because the elctrons orbit the nucleus in a wide orbit

Niels Bohr ageed with the planetary model of the atom, but also knew that it had a few flows. Using his knowledge of enrgy and quantum phyics he was able to perfect Rutherford's model. He was able to answer why the elcetrons did not collaspe into the nucleus

Bohr's Atomic Model (aka The Rutherford-Borh Model)
-Electrons orbit the nucleus in orbits that have a set size and energy
-The lower the energy of the electron, the lower the orbit
-This means thst as electrons fill up the orbitals, they will fill the lower energy level first.
-If thst energy level is fill(or at capasity), a new energy level will begin
-Radiation is when an electron moves from one level to another

Problem with this theory: Electros do not travel in a specific orbit or path

Robert Andrews Millikan was an American experimental physicist honored with the Nobel Prize for Physics in 1923 for his measurement of the elementary electronic charge and for his work on the photoelectric effect

Erwin Shrodinger was a revolutionary physicist who used Heisenberg's uncertainty principle to come up with the atomic model that we still use today

Shrodinger's Atomic Model (aka The Cloud Model)
-An electron does not travel in an exact orbit
-We can predict where it will probably be
-We cannot say for certain where it is, but only where it ought to be
-The type of probability orbit is dependen on the energy level described by Bohr