The Evolution of the Atomic Model

Vocabulary flashcards detailing the chronological development of atomic theory from ancient philosophy to modern quantum mechanics.

Atom

The smallest unit of matter that cannot be broken down chemically, consisting of a nucleus and electrons.

Democritus

A Greek philosopher around $400$ BCE who proposed that matter is made of tiny, indivisible particles called “atomos” without scientific evidence.

Atomos

A Greek term meaning indivisible particles, proposed by Democritus.

John Dalton

A scientist who proposed in $1803$ that all matter is made of atoms, atoms of an element are identical, and they combine in fixed ratios to form compounds.

Solid sphere model

The atomic model proposed by John Dalton reflecting the idea that atoms cannot be created or destroyed.

J.J. Thomson

A scientist who used the cathode ray tube experiment in $1897$ to discover negatively charged particles called electrons.

Electrons

Negatively charged particles discovered by J.J. Thomson.

Plum Pudding Model

J.J. Thomson’s model representing electrons embedded in a positive “soup.”

Ernest Rutherford

A scientist who conducted the gold foil experiment in $1911$ and concluded that the atom has a small, dense, positively charged nucleus.

Gold foil experiment

An experiment where alpha particles were shot at gold foil, showing that most passed through while some deflected, identifying a central nucleus.

Niels Bohr

A scientist who proposed in $1913$ that electrons orbit the nucleus in fixed paths or energy levels, explaining light emission from hydrogen.

Erwin Schrödinger

A scientist who used math equations in $1926$ to describe electron behavior in clouds rather than fixed orbits.

Orbitals

The concept introduced by Erwin Schrödinger describing electrons in probability clouds rather than fixed paths.

James Chadwick

A scientist who discovered neutrons in $1932$, completing the atomic structure puzzle.

Neutrons

Particles found in the nucleus with no charge that serve to stabilize the nucleus.

Modern Atomic Model

A model based on quantum physics where the nucleus contains protons and neutrons, and electrons exist in probability clouds or orbitals.