Overview
This lecture covers the historical development of atomic models, from early ideas to modern quantum mechanics, and explains the significance of each model.
Key Concepts: Matter and Atomic Particles
- Matter is anything with mass that occupies space.
- An atom is the smallest unit of matter and the building block of all substances.
- Protons are positively charged particles in the atom.
- Electrons are negatively charged particles around the nucleus.
- Neutrons are neutral particles discovered by James Chadwick in 1932.
Early Models of the Atom
- Democritus proposed that matter consists of indivisible particles called "atomos."
- John Dalton stated all elements are made of atoms; atoms of the same element are identical, and compounds are combinations of different atoms.
Discovery of Subatomic Particles
- J.J. Thomson discovered electrons and proposed the "plum pudding" model: electrons scattered in a positively charged sphere.
- Eugene Goldstein contributed to the discovery of protons.
The Nucleus and Planetary Models
- Ernest Rutherford identified the atom’s nucleus, with protons in the center and electrons scattered around the edge.
Refinement of Atomic Models
- Niels Bohr proposed electrons move in definite orbits (energy levels) around the nucleus, similar to planets orbiting the sun.
- Arnold Sommerfeld modified Bohr's theory to include elliptical orbits, not just circular ones.
The Quantum Mechanical Model
- Erwin Schrödinger developed the quantum mechanical model, stating that electrons occupy regions (orbitals) where they are most likely found.
- In this model, electron position depends on energy, and their movement is described by wave mechanics, not fixed paths.
Key Terms & Definitions
- Atom — Smallest unit of matter participating in chemical reactions.
- Proton — Positively charged particle in the atom’s nucleus.
- Electron — Negatively charged particle orbiting the nucleus.
- Neutron — Neutral particle in the atom’s nucleus.
- Nucleus — Center of the atom containing protons and neutrons.
- Orbit/Orbital — Region where an electron is likely to be found.
- Quantum Mechanics — Study of particles’ behavior at atomic and subatomic levels.
Action Items / Next Steps
- Review each atomic model and note key differences.
- Prepare to describe how Bohr’s model improved upon Rutherford’s model.
- Complete any assigned readings or homework on atomic history.