Overview
This lecture covers the history and development of atomic models, their key contributors, and how our understanding of the atom has evolved over time.
Key Concepts in Chemistry
- Matter is anything that has mass and occupies space.
- Atom is the smallest unit of matter and the building block of matter.
- Protons are positively charged particles found in the nucleus.
- Electrons are negatively charged particles found outside the nucleus.
- Neutrons are uncharged particles discovered by James Chadwick in 1932.
Key Contributors to Atomic Theory
- Eugene Goldstein discovered the idea of positively charged protons.
- Democritus named the smallest piece of matter "atomos," meaning indivisible.
- John Dalton stated that all elements are made of atoms; atoms of the same element are identical, and compounds form from different atoms.
- J.J. Thomson discovered electrons and proposed the "plum pudding" model with electrons scattered in a positive substance.
- Ernest Rutherford showed protons are in the nucleus, with electrons orbiting around it.
- Niels Bohr improved previous models by placing electrons in specific energy levels or orbits.
- Arnold Sommerfeld modified Bohr’s model by introducing elliptical orbits for electrons.
- Erwin Schrödinger developed the quantum mechanical model, describing electrons as existing in probabilistic clouds rather than fixed orbits.
Advances in Atomic Models
- Early models depicted atoms as indivisible and solid.
- Thomson’s model introduced internal structure with electrons.
- Rutherford’s model identified the nucleus.
- Bohr’s model explained energy levels and orbits.
- Sommerfeld added elliptical orbits.
- Schrödinger's quantum model describes electrons in probable locations using wave mechanics.
Key Terms & Definitions
- Atom — Smallest unit of matter involved in chemical reactions.
- Proton — Positively charged particle in the atomic nucleus.
- Electron — Negatively charged particle around the nucleus.
- Neutron — Uncharged particle in the nucleus.
- Nucleus — Dense center of an atom containing protons and neutrons.
- Energy Level — Specific paths where electrons orbit in the Bohr model.
- Quantum Mechanics — Branch of physics describing the behavior of particles at atomic scales.
Action Items / Next Steps
- Review the contributions of each scientist to atomic theory.
- Be ready to describe how Bohr’s model improved Rutherford’s model.
- Prepare to discuss the significance of atomic model development in modern science.