Evolution of Atomic Models

This set of vocabulary flashcards covers the historical development of atomic theories from Ancient Greece to the modern quantum-mechanical model.

Democritus

A Greek philosopher who proposed that matter is made of tiny, eternal, and invisible particles called "atoms" that cannot be further divided.

Atom

Derived from a Greek word meaning "indivisible," it refers to the smallest unit of matter.

John Dalton

Scientist in the early $19th$ century who formulated the first scientific atomic theory, proposing that atoms are indestructible and combine in defined proportions.

Billiard Ball Model

John Dalton's conceptualization of the atom as a solid, massive sphere.

J. J. Thomson

Scientist who discovered the electron through cathode ray tube experiments and proposed the "plum pudding" model.

Electron

A subatomic particle with a negative charge discovered by J. J. Thomson at the end of the $19th$ century.

Plum Pudding Model

Atomic model proposed by Thomson describing the atom as a positive sphere with negative electrons embedded inside like raisins in a pudding.

Ernest Rutherford

Scientist who conducted the gold foil experiment and concluded that the atom is mostly empty space with a dense, positively charged center.

Gold Foil Experiment

An experiment where alpha particles were fired at a thin gold sheet, revealing that most particles passed through while a few deflected or bounced back.

Nucleus

A very small, dense region at the center of the atom discovered by Rutherford, where most of the mass and positive charge are concentrated.

Niels Bohr

Scientist who in $1913$ proposed that electrons move in specific orbits or energy levels around the nucleus without losing energy.

Energy Levels

Specific orbits where electrons reside; they only absorb or release energy when jumping from one of these levels to another.

Erwin Schrödinger

Scientist who developed the quantum-mechanical model, proposing that electrons move in complex ways rather than fixed orbits.

Quantum-Mechanical Model

The modern atomic model that calculates the probability of finding an electron in a specific region rather than tracking a fixed path.

Orbital

A region in space where there is a high probability of finding an electron, according to the modern atomic model.

James Chadwick

The scientist who discovered the neutron, a subatomic particle with no electrical charge located in the nucleus.

Neutron

A particle found in the nucleus with no electrical charge, discovered by James Chadwick.

Proton

A positively charged particle whose quantity determines which specific chemical element an atom belongs to.