Understanding of the atom

Origin of the atom

460

Democritus, a greek philosopher, proposed a theory that if you cut up matter into smaller and smaller pieces then eventually you will not be able to cut it any smaller. He thought that the atomos would have the same properties as the original piece. He was then set back by the widely accepted but false views of Aristotle, in 460BC.
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Air can push down

Jul 23, 1643

Evangelista Torricelli found that air could push down mercury in a tube.
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What is air?

Jul 27, 1740

Daniel Bernoulli, proposed that air c is made up of tiny particles that are so small that we cannot feel or see them. He thought that they were loosly packed together.
Matter

Many different particles make up matter

Jul 27, 1773

Joseph Priestley found that he could split mercury calx stones into liquid mercury and a gas later called oxygen by heating it.

Conservation of Mass

Jul 27, 1778

Antoine Lavoisier, through experiments in which he renamed hydrogen and oxygen, found that mass is not lost or gained during a chemical reaction. He also found out that hydrogen reacts with oxygen to create water.

Dalton's atomic theories

Jul 27, 1803

John Dalton proposed that all matter is made of indivisible atoms; and that all atoms of the same element are the same, while different elements have different properties. He also proposed that chemical reactions are the combination of atoms, and that when elements react to form compounds that the compounds are of set ratios. This is called the Law of Definite Proportions.

Electrolysis

Jul 27, 1832

Michael Faraday described the splitting of molecules with electricity as electrolysis and developed the laws of electrolysis.
Atomic Structure Timeline

Planck's constant

Jul 27, 1900

Max Planck used Planck's constant to explain how certain amounts of energy were omitted when the object resonates light. He used the equation: E=hv, energy omitted equals Planck's constant multiplied by the frewuency of light.

Plum Pie Model of the Atom

Jul 28, 1904

J.J. Thomson proposed his model of the atom which consisted of a round positively charged mass with negatively charged particles distributed throughout.
History of Atomic Theory

E=mc^2

Jul 27, 1905

Albert Einstein proposed the equation that determined the amount of energy omitted in a nuclear reaction.

Oil drops

Jul 27, 1909

R.A.Millikan's oil drop experiment helped to determine the mass and charge of an electron

Gold foil

Jul 27, 1911

Ernest Rutherford fired alpha particles at goldfoil and through this summarized that very dense, very small and positively charged.

Isotopes

Jul 27, 1919

Aston predicted the existence of isotopes by using a mass spectrograph.

Bohr model of the atom

Jul 27, 1922

Neils Bohr proposed his model of the atom which was composed of successful electron orbits.

How can it be both a particle and a wave?

Jul 27, 1923

Joseph de Broglie held the view that all objects held both particle and wave natures. He said this was only really apparent for extremely light particles such as electrons.

Principle of Indeterminancy

Jul 27, 1927

Heisenberg proposed a theory that stated that the observer cannot know the position and velocity of a particle.

Antiparticles

Jul 27, 1930

Paul Dirac proposed the existence of antiparticles. This was then confirmed for the electron and proton in 1932 and 1955 respectively

Schrodinger

Jul 27, 1930

Schrodinger used "wave mechanics" to help to describe the atom

The neutron

Jul 27, 1932

James Chadwick used beams of alpha particles to discover the other part of the nucleus

Nuclear Reactor

Jul 27, 1942

Enrico Fermi supervised the design and creation of a self sustaining chain reaction that resulted in the release of nuclear energy.