Development of the Atomic Model

Vocabulary flashcards outlining the historical development of the atomic model from Democritus to Niels Bohr.

Democritus

A Greek philosopher who proposed around 400 BC that atoms are indivisible and represent the smallest quantities of matter, with atoms of different substances differing in characteristics.

John Dalton

An English chemist who conducted experiments in the early 1800s that revived Democritus's ideas and led to the widespread acceptance of the atom.

Billiard Ball Model

Dalton's atomic model proposing that all matter is composed of indivisible, spherical atoms, where atoms of an element are identical and atoms of different elements combine to form compounds.

Electron

The first subatomic particle discovered in 1897 by Joseph John Thomson, consisting of negatively charged particles with 1800 times less mass than a hydrogen atom.

Plum Pudding Model

J. J. Thomson's model of the atom, which depicts an overall neutral sphere of positive charge with negatively charged electrons dotted around inside.

Hans Geiger and Ernest Marsden

Students of Ernest Rutherford who carried out the Gold Foil Experiment at Manchester University in 1909, disproving the plum pudding model.

Gold Foil Experiment

A 1909 experiment in which alpha particles were fired at thin gold foil; while most passed through, some deflected or bounced back, demonstrating that positive charge is concentrated in a central area.

Nucleus (Atomic)

The small, dense, positively charged centre of an atom named by Ernest Rutherford in 1911 that contains all positive particles and most of the atom's mass.

Planetary Model (Nuclear Model)

Rutherford's 1911 model of the atom stating that atoms are mostly open space with a dense positive nucleus orbited by electrons like planets around a solar system.

Niels Bohr

A Danish scientist who in 1913 applied mathematical models to resolve the flaw in Rutherford's model where orbiting electrons would spiral into the nucleus.

Bohr Model

An atomic model proposing that electrons travel around the nucleus in fixed energy levels or shells, each accommodating a specific maximum number of electrons.