History of the Atomic Model

Democritus 450 BC

450

Stated that all things are made of atoms.
Invisible and indestructible.
Empty space between atoms.
Atom have rounds shape.
Solid Sphere Model.

John Dalton

Jan 1, 1803

All atoms have characteristic weight and mass.
An element is made of all identical atoms together.
Chemical reactions involve rearranging atoms.
Stated general information on the atom.
Solid Sphere Model

JJ Thompson

Jan 1, 1897

Discovered electrons.
Discovered that atoms can be split.
Atoms are made of postive charged cores with negative particles PLUM PUDDING:
- Electrons are the negative plums in positive pudding
- Plum Pudding model made before nucleus discovered

Albert Einstein

Jan 1, 1905

Proposed the quantum of light.
States that light behaves like a particle but also has wave lengths which gives it a dual nature.
Showed how energy and mass equal through his E=mc^2

Ernest Rutherford

Jan 1, 1911

Concluded on dense small nucleus.
Positively charged due to neutrons (neutral) and protons (positive)
Rutherford Atomic model shows positive nucleus in center of atom.

Robert Millikan

Jan 1, 1912

Discovered the negative charge of an electron.
Through his "oil drop" expirement.

Niels Bohr

Jan 1, 1913

Created a physical picture of the atomic structure.
With improvements, Bohr's pictures are still used to show physical and chemical characteristics of atom.
Model shows nuclueus and the 3 shells of electrons.
Each shell shows max number of electrons possible in shell

Louis de Broglie

Jan 1, 1924

Stated that electrons could act as wave lengths.
Was the basis of what is now Wave Mechanics Theory.
This explained why electrons do things we couldn't explain why before.

Wolfgang Pauli

Jan 1, 1925

States that no two electrons in an atom have the same four quantum numbers.
Also stated that as an elctron orbits the nucleus it should also spin
Contributes the the planetary atomic model.

Erwin Schrödinger

Jan 1, 1926

Inferred that electrons were continuous clouds.
Created wave mechanics as a mathematical model to show the distribution of electrons in an atom.
Worked off of Louis de Broglie's work.

James Chadwick

Jan 1, 1932

Discovered neutron.
Atomic particle with neutral charge and around same mass as proton.
Found in nucleus.

Werner Heisenberg

Jan 1, 1940

Studied the pattern of electrons.
Inferred that electrons orbit the nucleus.
Helped form the Planetary Atomic Model.
Helped clarify the modern veiw of an atom.