1. The History of Atomic Theory
Chapter 4.1 Notes The Atom
The History of Atomic Theory

2. Composed of 3 main subatomic particles: protons, electrons, and neutrons.

3. John Dalton
In the early 1800’s, Dalton proposed that atoms are tiny, indestructible particles with no internal structure.

4. All elements are composed of indivisible particles called atoms.
Atoms of the same element are identical, and different from any other element.
Atoms of different elements can physically mix or chemically combine in whole-number ratios to from compounds.
Chemical reactions occur when atoms or separated, joined, or rearranged. However, atoms never change from one element to another as a result of a chemical reaction.

5. J.J. Thomson (1897) Discovered the electron.
Developed the ‘plum pudding’ model where electrons are embedded in a sphere of positive electrical charges.

6. Hantaro Nagaoka (1904)
A Japanese physicist who suggested that atoms have a central nucleus.
Electrons move in orbit like the rings around Saturn.

7. Ernest Rutherford (1908) Discovered the nucleus.
Electrons move around the nucleus at equal distances but on different paths.

8. Niels Bohr (1913)
Electrons move in a circular orbit at fixed but different distances from the nucleus which has a positive charge.
This model worked with hydrogen but failed with larger atoms.

9. Erwin Schrodinger (1922)
Developed a mathematical equation that describes the motion (not pathway) of electrons and where they are likely to be found.
Called the electron cloud model.
Dark blue= more likely that electron is present

10. Louis de Brogile (1925)
Proposed that electrons have wave-like properties.
Few years later, experimental evidence supports his idea.