History of Atomic Models

Vocabulary review covering the historical progression of atomic theories and models from Democritus and Dalton to Thompson, Rutherford, Bohr, and the modern Quantum Mechanical Model.

Democritus (400 BC)

Greek philosopher who proposed that matter is indivisible, referring to these fundamental units as atomos.

Atomos

The concept introduced by Democritus in 400 BC meaning indivisible matter.

Dalton's Atomic Theory (1803)

A five-part theory stating: (1) all elements are composed of indivisible atoms that cannot be broken down further, (2) atoms of a given element are similar in physical and chemical properties, (3) atoms of different elements differ in properties, (4) atoms combine in simple whole-number ratios to form compounds, and (5) chemical reactions combine, separate, or rearrange atoms, but never create, destroy, or change them.

Solid Sphere Model

Atomic model associated with Dalton (1803) that represents the atom as a solid, indivisible sphere.

Thompson (1897)

Scientist who discovered the electron and proposed the Plum Pudding Model of the atom.

Plum Pudding Model

Atomic model proposed by Thompson in 1897, featuring negatively charged electrons embedded within a spherical positive charge.

Millikan (1909)

Scientist who discovered the charge of electrons.

Rutherford (1911)

Scientist who discovered that the atom contains a positively charged nucleus with electrons moving around it.

Rutherford's Atomic Model

1911 model demonstrating an atom with a central, positively charged nucleus and orbiting electrons moving around it.

Bohr (1912)

Scientist who developed the Planetary Model, proposing that electrons orbit around the nucleus much like planets orbit around the sun.

Planetary Model

Atomic model introduced by Bohr in 1912 depicting electrons traveling in circular shells or energy levels around a positively charged nucleus.

Quantum Mechanical Model

Today's atomic model, which predicts the probability of electron locations and paths within an electron cloud surrounding the nucleus.

Electron Cloud

A region surrounding the nucleus in the Quantum Mechanical Model where the locations and paths of electrons are described in terms of probability.