In 440BC, a greek philosopher named Democritus came up with the concept of an atom.
Democritus said that atoms were small, hard particles that could not be divided("uncuttable")
Atom- the smallest parcel into which an element can be divided and still be the same substance.
Atomic theory based on observations gathered from many experiments from combining elements.
All substances are made of atoms. Atoms are small particles that can not be created, divided, or destroyed.
Atoms join with other atoms to make new substances.
Thomson experimented with a Cathode Ray tube.
Thomson called the negatively charged particles corpuscles.
Thomson's Plum Pudding Model
His Plum Pudding model showed a possible structure of the atom with the negative charges.
Rutherford discovered that the atom had a small. dense nucleus than contained positive charges.
Gold foil experiment- aimed charged particles at a thin sheet of gold foil.
A particle that actually hit the nucleus would be deflected almost straight back.
Rutherfords's "Planetary Model"
- The atom is mostly empty space through which electrons travel.
- The atom has a small, dense, positively charged nucleus (most of the mass is in the nucleus).
Electrons travel around the nucleus like planets around the sun.
In 1913, Neils Bohr determined that electrons traveled around the nucleus in definite paths.
He also discovered that electrons could jump from a path in one level to a path in another level.
Current Theory- Electron Clouds ModelSchrodinger an Heisenberg
Schrodinger and Heisenberg explained that electrons do not travel in definite paths.
Electrons cannot be predicted.
The current theory suggests that electrons are found in regions called electrons clouds.