Thomson's Electron Discovery and Atomic Model

JJ Thomson's groundbreaking work in 1897 led to the discovery of electrons using Cathode Ray Tubes. His research fundamentally changed our understanding of atomic structure.

Highlight: The plum pudding model depicted atoms as positive spheres with embedded negative electrons.

Example: Thomson used the analogy of chocolate chip cookies to explain his atomic model.

Vocabulary: Crooke's Tube - a glass tube filled with gases used to study electron behavior.

Definition: Electrons are negatively charged subatomic particles with very small mass compared to atoms.

Rutherford's Model and Nuclear Discovery

Rutherford's famous gold foil experiment (1909) revolutionized atomic theory by revealing the nuclear structure of atoms.

Highlight: The experiment showed that atoms are mostly empty space with a dense, positively-charged nucleus.

Example: Alpha particles passing through gold foil demonstrated nuclear structure through their deflection patterns.

Definition: The nuclear model places protons in a central nucleus with orbiting electrons.

Vocabulary: Alpha particles are positively charged particles used in Rutherford's experiment.

James Chadwick's discovery of neutrons in the early 1900s completed our basic understanding of atomic structure.

Definition: Neutrons are neutral particles with mass equal to protons (1 amu).

Highlight: The discovery of neutrons explained the extra mass observed in atoms and helped complete our understanding of atomic structure.

Rutherford's Nuclear Model and Chadwick's Neutron

The development of the nuclear model came through Rutherford's famous gold foil experiment.

Highlight: Most alpha particles passed through the gold foil, but some were deflected, leading to the discovery of the nucleus.

Definition: The nuclear model proposed a dense, positively charged center (nucleus) surrounded by electrons.

James Chadwick's discovery of neutrons completed our understanding of basic atomic structure.

Vocabulary: AMU (Atomic Mass Unit) - Where 1 proton = 1 neutron = 1 amu.

Early Atomic Theory and Dalton's Contributions

The journey of atomic theory begins with Greek philosophers around 400 BC. Democritus and Leucippus developed the concept of atomos using the Greek philosophers analogy legos to explain how the world is constructed from tiny, indivisible particles.

Definition: Atomos were considered the smallest, indivisible particles of matter.

John Dalton's atomic theory (1800) built upon three fundamental laws:

Highlight: The Law of Conservation of Matter states that matter cannot be created or destroyed, only transformed.

Example: Lavoisier's experiment with burning magnesium demonstrated this law: 2Mg + O₂ → 2MgO

Vocabulary: Law of Definite Proportion - compounds have fixed molecular formulas with whole number ratios.

Quote: "All matter is composed of tiny, indivisible, and indestructible particles called atoms."