Development of Atomic Models

Leucippus and Democritus

Atomos, meaning uncuttable

Leucippus and Democritus

Atom as solid indivisible sphere

Aristotle (and Others)

Matter is made up of four elements

John Dalton

Solid Sphere (Billiard Ball) Model

John Dalton

Atom as solid sphere but NOT indivisible

Humphry Davy

Elements of a chemical compound are held together by electrical forces

Michael Faraday

Relationship between the amount of electricity used in electrolysis and the amount of chemical reaction that occurs

George Stoney

"Electrons" → Electric ions

Joseph John Thomson (JJ Thomson)

Cathode-Ray Tube Experiment, the most convincing evidence of electrons

Joseph John Thomson (JJ Thomson)

Plum pudding model

Robert Millikan

Oil-drop Experiment

Robert Millikan

He determined the charge of electrons

Hantaro Nagaoka

Saturn-like model

Eugen Goldstein

Canal Rays Experiment

Ernest Rutherford

The Scattering Experiment, Gold Foil Experiment

Ernest Rutherford

He discovered the protons and the nucleus

Ernest Rutherford

Nuclear Model

H.G.J. Moseley

He studied X-rays given off by various elements.

H.G.J. Moseley

"The number of protons in the nucleus of an atom determines its identity; this number is known as the atomic number of that element."

J. Chadwick

bombardment of beryllium with high-energy alpha-particles produced NEUTRONS

J. Chadwick

He discovered neutrons

Niels Bohr

described the electron of a hydrogen atom as revolving around its nucleus in one of a discrete set of circular orbits.

Bohr's Planetary Model

This model shows that each orbit thus corresponds to a definite energy level for the electron

Bohr’s Planetary Model

This model shows that when an electron is excited from a lower energy level to a higher one, it absorbs a definite (quantized) amount of energy

Bohr's Planetary Model

This model shows that electrons occupy only certain energy levels in atoms

Louis de Brogli

proposed the idea of wave-like nature of electrons

Louis de Brogli

Electrons can be treated as waves more effectively than as small compact particles traveling in circular or elliptical orbits

Werner Heisenberg's Uncertainty Principle

A principle that states that: for electrons, it is not possible to determine the exact momentum and the exact position at the same moment in time

Erwin Schrödinger's Wave Equation

It estimates the position of electrons and quantifies energy levels

Atomic Orbitals

A region of space in which the probability of finding an electron is high

Erwin Schrödinger

The Modern Atomic Model

Erwin Schrödinger

Electron Cloud Model

Erwin Schrödinger

Quantum Mechanical Model