Historical Development of the Atomic Model

These flashcards provide a historical overview of the development of the atomic model, from early philosophical concepts to the modern quantum mechanical understanding.

What is an atom?

The smallest unit of an element that still retains the properties of that element.

Who was the Greek philosopher who first proposed the idea of "atomos"?

Democritus (c. 400 BC)

What does the Greek word "atomos" mean?

Indivisible

What was the main limitation of Democritus' atomic idea?

His idea was not based on experiments, so many people did not accept it.

Which four elements did Aristotle believe made up all matter?

Earth, Water, Air, and Fire

How long did Aristotle's ideas about matter remain widely accepted?

Nearly 2,000 years

What are the key postulates of John Dalton's (1803) Modern Atomic Theory?

Matter is made of atoms; atoms cannot be divided; atoms of the same element are identical; different elements have different atoms; atoms combine to form compounds.

What is another name for John Dalton's atomic model?

The Solid Sphere Model

Which experiment led J. J. Thomson to the discovery of the electron in 1897?

The Cathode Ray Tube Experiment

How is J. J. Thomson's "Plum Pudding Model" described?

A positive sphere with negatively charged electrons embedded throughout.

What were the two major discoveries Ernest Rutherford made through the Gold Foil Experiment in 1911?

1. Most of the atom is empty space. 2. Positive charge is concentrated in a tiny nucleus.

Which model is associated with Ernest Rutherford?

The Nuclear Model

What did Niels Bohr propose about electron movement in his 1913 Planetary Model?

Electrons move around the nucleus in fixed energy levels and absorb or release energy when moving between levels.

What regions are electrons found in according to Erwin Schrödinger’s (1926) Quantum Mechanical Model?

Electron clouds or orbitals

What did James Chadwick discover in 1932?

The neutron, a neutral particle located in the nucleus.

How did the discovery of the neutron explain isotopes?

It explained why atoms of the same element can have different masses.