Understanding Atomic Theory

Early Concepts of Atoms

Leucippus and Democritus (ca. 2500 years ago):
- Proposed matter is composed of tiny, indivisible particles called 'a-tomos' (uncuttable).
- Believed substances were made up of their own unique particles (e.g., iron of iron particles).
- Conceptualized atoms' forms reflecting their properties.

Discharge Tube Experiments (1870s):
- Gas-filled tubes with electrodes emitted light when electrified.
- Cathode Rays: Discovered as negatively charged.
Eugen Goldstein (1886):
- Identified rays from positive electrode, implying positive charge in matter.
J.J. Thomson:
- Determined cathode rays were composed of particles much lighter than hydrogen.
- Named these particles electrons, proposing the 'plum pudding model' (electrons in a positive matrix).

Ernest Rutherford (1909):
- Gold foil experiment demonstrated that atoms have a small, dense nucleus.
- Identified protons as positively charged particles in the nucleus.

Niels Bohr:
- Applied mathematical principles to atomic structure.
- Proposed electrons orbit the nucleus at specific energy levels, known as the 'planetary model'.

Werner Heisenberg:
- Introduced the uncertainty principle, complicating precise electron position and momentum measurement.
- Developed quantum theory, suggesting electrons have wave-particle duality.
Modern Quantum Model:
- Electrons exist in probability clouds called orbitals.

Atomic theory evolved through contributions of many scientists over centuries.
Current models are based on probability and experimental evidence.
Ongoing research and questioning remain crucial for future developments in atomic theory.