Atomic Theory

Aristotle

340

Aristotle believed that all matter was made of five main things; earth, air, fire, water, and Aether. Aether was what made up the galaxy, stars, and outer space. Aristotle was very personable and his theory was widely accepted for thousands of years.

Democritus

450

Proposed atomic theory:
*Everything is made of atoms
*Atoms of same element are the same and atoms of different atoms are different
*All atoms had different shapes which determined the element's characteristics
*Atoms could combine with other atoms

Alchemists

Apr 23, 1300

Alchemists coined the term element and analyzed matter with special equipment as well as improved techniques of distillation/crystallization.

Benjamin Franklin

Apr 23, 1752

Did extensive studies and experiments on static electricity. Made discoveries about electricity by observing lightning.

Luigi Galvani

Apr 23, 1780

He was the pioneer of bioelectromagnetics. He studied how electrical currents and electrons were used in the body, specifically in the nervous system. Conducted an experiment and found that a dead frog's leg would move when struck with electrons.

Antoine Lavoisier

Apr 23, 1785

Came up with the law of conservation of mass. Determined that the mass of the rectants and products would be equal in any chemical reaction.

Joseph Proust

Apr 23, 1799

First scientist to state the theory of constant composition. Discovered that all chemical compounds will have the same composition of elements.

Alessandro Volta

Apr 23, 1800

He was the inventor of the first electrical battery and the discoverer of methane. His invention allowed scientists to produce steady flows of electric current for the first time.

John Dalton

Apr 23, 1803

Proposed his atomic theory which has been modified slightly for use in present day.
*All matter is made of atoms
*All atoms of the same element have the same size and mass
*Atoms cannot be created, divided, or destroyed
*Atoms of different elements combine in whole number proportions
*In chemical reactions, atoms are rearranged

Avogadro

Apr 23, 1811

Avogadro hypothesized that if the pressure and temperatures were the same, then equal volumes of gases would contain equal numbers of molecules. Also hypothesized that simple gases were not formed out of solitary atoms but were compound molecules.

Michael Faraday

Apr 23, 1832

Used electrolysis to split molecules with electricity. He was the first person to associate electricity and atoms.

Dmitri Mendeleev

Apr 23, 1869

Arranged elements by properties and developed the periodic law. Discovered that elements "were periodic functions of the their atomic weights".

William Crookes

Apr 23, 1879

Crookes experimented with sending an electric current through a tube with electrodes at either end. The particles could penetrate though sheets of metal which led him to conclude that electrons were smaller than atoms and molecules.

Wilhelm Roentgen

Apr 23, 1895

First person to make and detect EMR in the wavelength of X-rays. Invented the X-ray generator.

Henry Becquerel

Apr 23, 1896

Discovered radiocativity through the use of unexposed photo film and uranium. He discovered that uranium naturally emitted radioactive rays without having to sit in the sun at all which led to his conclusion that the uranium was emitting X-rays.

J.J. Thomson

Apr 23, 1897

Used experiments to determine the chage to mass ratio of an electron. Also developed the plum pudding model of an atom.

Marie and Pierre Curie

Apr 23, 1898

Studied the elements uranium and thorium extensively because they were interested in their spontaneous decay which they named radioactivity. They also discovered the elements polonium and radium.

Frederick Soddy

Apr 23, 1900

Contributed information about the chemistry of radioactive atoms and also investigated the origin and nature of isotopes.

Albert Einstein

Apr 23, 1905

Developed the equation E=mc2 Determined that the speed of light was always constant and that mass and kinetic energy were equal.

Hans Geiger

Apr 23, 1906

Invented the Geiger counter to measure radiation. He was the first person to create a device that successfully measured individual alpha particles.

Max Planck

Apr 23, 1907

Planck was able to determine the relationship between energy and the frequence of radiation. Used quantum theory and published two books about thermodynamics.

Robert Millikan

Apr 23, 1909

Millikan performed the oil drop experiment where the oil droplet had a small charge and Millikan would measure how strong the electric field had to be to stop the drop from reaching the bottom. From this information, he determined the change of the electron.

Ernest Rutherford

Apr 23, 1909

Coined the terms alpha and beta radiation. Found that radiation was emitted from uranium and thorium and directed the gold foil experiment.

Niels Bohr

Apr 23, 1913

Bohr modified Rutherford's model because he believed that the electrons would travel in a fixed circle around the nucleus. Bohr also believed that the electrons could jump between orbitals.

Louis deBroglie

Apr 23, 1924

Suggested that electrons, like light, could travel in both particles and waves. His ideas explained the restricted orbitals that the electrons were known to travel in.

Werner Heisenberg

Apr 23, 1925

Used mathematics to describe the movement of electrons in their orbitals. He also used quantum mechanics to contribute to the atomic theory.

Erwin Schrodinger

Apr 23, 1926

Concluded that electrons are in continuous clouds. He used wave mechanics as a mathematical model of he atom.

Paul Dirac

Apr 23, 1930

Theoretical physicist who contributed to the developing quantum mechanics and quantum electrodynamics. Derived important mathematical equations that helped explain the atom.

James Chadwick

Apr 23, 1932

Conducted an experiment where he shot alpha particles at beryllium atoms and found that a beam was given off when this occured. He tested the beam with a magnet and found that it did not have a charge; this beam was made of neutrons.

Lise Meitner

Apr 23, 1938

Lead a team of scientists who discovered nuclear fission of uranium when they performed an experiment and it absorbed an extra neutron.

Glenn Seaborg

Apr 23, 1941

He synthesized, discovered, and investigated ten transuranium elements.

Enrico Fermi

Apr 23, 1942

Created the world's first nuclear reactor using gathered information about fission and fusion.