Atomic Theory: Key Terms and Models

Vocabulary flashcards covering the major terms and concepts from the lecture notes on atomic theory and its historical development.

Bohr model

An atomic model in which electrons occupy fixed energy levels (orbits) around the nucleus; energy levels are quantized.

Democritus

Ancient Greek philosopher who proposed matter is composed of indivisible particles called atomos; atoms are infinite in number and always moving.

atomos

Greek word meaning 'not to be cut'; the smallest piece of matter proposed by Democritus.

Bowling Ball Model

Dalton's early atomic theory describing atoms as solid, indivisible balls; atoms of the same element are identical; compounds form by joining atoms.

John Dalton

English chemist who proposed that elements are composed of atoms; atoms are indivisible, atoms of the same element are identical, and compounds form by combining atoms.

Plum Pudding Model

Thomson's atomic model with a positively charged sphere containing negatively charged electrons dispersed like raisins in a pudding.

Electron

Negatively charged subatomic particle; discovered by Thomson; located in atoms and smaller than atoms.

Corpuscles

Thomson's historical term for electrons.

Crookes tube (cathode ray tube)

Glass tube used in early experiments to study cathode rays, leading to the discovery of electrons.

Ernest Rutherford

Physicist who proposed the Nuclear Model after the gold foil experiment; showed atoms are mostly empty space with a tiny dense nucleus.

Nucleus

Tiny, dense, positively charged center of the atom; the center around which electrons orbit.

Nuclear Model

Rutherford's atomic model with a central nucleus and orbiting electrons; most of the atom is empty space.

Niels Bohr

Danish physicist who placed electrons in fixed energy levels around the nucleus; introduced the planetary orbits concept.

Energy level

Fixed distance from the nucleus where electrons reside; in Bohr's model, electrons occupy specific energy levels.

Erwin Schrödinger

Austrian physicist who developed the quantum mechanical model, using equations to describe electron probabilities instead of fixed paths.

Quantum mechanical model

Modern atomic model describing electrons as existing in probability clouds rather than definite orbits.

Electron cloud

Region around the nucleus where electrons are most likely to be found; density corresponds to probability of presence.

Sub-energy levels

Divisions within energy levels that describe finer arrangements of electrons in different orbitals; introduced by the quantum model.

Aristotle

Greek philosopher who supported the four-element theory (earth, fire, air, water) and opposed atomos, delaying acceptance of atomic theory for about 2000 years.

Plato

Greek philosopher whose elements theory contributed to the suppression of early atomic ideas; part of why atomos was forgotten for centuries.