Atomic Theory
John Dalton: Early 1800s
~ discovered 4 parts of atomic theory
1. All elements are composed of atoms that cannot be divided
2. All atoms of the same element are exactly alike and have the same mass
3. An atom of one element cannot be changed into an atom of a different element.
Atoms cannot be created or destroyed in any chemical change, only rearranged.
4. Every compound is composed of atoms of different elements, combined in a specific
ratio.
Model:
J.J. Thomson: 1897
~ Discovered electrons (negatively charged particles)
~ Assumed there was a positive charge because atoms are neutral.
~ “Berry Muffin”, “Chocolate Chip” or “Plum Pudding” model - negative charge floating randomly
in a mass of positiveness.
Model:
Green is the positiveness and the blue is the random placement of negative electrons
Ernest Rutherford: 1911
~Gold Foil Experiment: Positive charged particles were shot at a thin piece of gold foil. Majority
of the particles went straight through the foil. Some bounced off in opposite directions.
~ Discovered: There must a dense mass in the middle that is deflecting the positive beam
(nucleus)
~ Positively charged particles are in the middle (protons)
Experiment:
Model:
Niels Bohr: 1913
~ Discovered electrons have a specific amount of energy, leads them to have certain orbitals
~ Think of it like an onion!
Model:
Cloud of Electrons: 1926
~ Electrons have different energies but it is more like a cloud.
~ Cloud represents the possibility of where the electron is at that energy level.
Model:
James Chadwick - 1932
~ Modern atomic model
~ Discovered neutrons in the nucleus- neutral charged particles
Model: