History of the Atom – Key Vocabulary

Vocabulary flashcards summarizing scientists, experiments, particles, and concepts in the development of the atomic model.

John Dalton (1803)

Proposed that all matter was made of indivisible atoms

J. J. Thomson (1897)

Discovered the electron and proposed plum pudding model

Plum Pudding Model

Early atomic model depicting electrons embedded in a diffuse, positively charged sphere.

Ernest Rutherford (1911)

Performed the gold foil experiment, discovered the nucleus, and showed that most of the atom is empty space.

Gold Foil Experiment

Rutherford’s scattering experiment that revealed a small, dense, positively charged nucleus inside the atom.

Nucleus

Central, dense region of the atom containing protons (and later found neutrons) with a positive charge.

Niels Bohr (1913)

Suggested electrons occupy fixed energy levels (shells) around the nucleus, explaining atomic emission spectra.

Energy Levels (Shells)

Fixed orbits around the nucleus where electrons reside, as proposed in Bohr’s atomic model.

Atomic Emission Spectra

Distinctive light patterns produced when electrons drop to lower energy levels, supporting Bohr’s model.

James Chadwick (1932)

Discovered the neutron, completing the sub-atomic particle picture of the nucleus.

Neutron

A neutral sub-atomic particle found in the nucleus alongside protons; discovered by Chadwick.

Modern Atomic Model

Current understanding featuring a nucleus of protons and neutrons surrounded by electrons in orbitals or clouds.

Quantum Mechanics

Branch of physics underlying the modern atomic model, describing probabilistic electron distributions and energy levels.