THE HISTORY OF THE THE HISTORY OF THE ATOMATOM

Greek Philosophers (400 B.C.)Greek Philosophers (400 B.C.)

Aristotle- believed the everything was made of the Aristotle- believed the everything was made of the 4 elements (air, fire, water, and land). Each 4 elements (air, fire, water, and land). Each substance contained a varying portion of each substance contained a varying portion of each element.element.

Democritus-believed everything was made of Democritus-believed everything was made of invisible and indivisible particles called “invisible and indivisible particles called “atomus” atomus” = = ATOMSATOMS

Ben Franklin -1748Ben Franklin -1748

Determined there wereDetermined there were positive positive and and negativenegative charges in nature.charges in nature.

Antoine Lavoisier-1790Antoine Lavoisier-1790

Law of conservation of matter- Law of conservation of matter- matter ismatter is neither created nor destroyed in anyneither created nor destroyed in any processprocess ( (you did anyou did an experiment with the test experiment with the test tube and the flasktube and the flask))

Joseph Louis Proust - 1799Joseph Louis Proust - 1799

Law of constant composition - Law of constant composition - any sample of any sample of aa given compound always contains the given compound always contains the samesame percent of each element by mass.percent of each element by mass.

John Dalton-1803John Dalton-1803 Created the Created the Atomic Theory of MatterAtomic Theory of Matter

Contains 4 postulateContains 4 postulate::1.1. Each element is made of invisible and indivisible Each element is made of invisible and indivisible

particles called atoms. (particles called atoms. (DemocritusDemocritus) ) wrongwrong

2.2. All atoms of an element are identical. All atoms of an element are identical. wrongwrong

3.3. Atoms can not be created or destroyed in a Atoms can not be created or destroyed in a reaction.reaction.

((LaviosierLaviosier))

4. A given compound always has the same relative 4. A given compound always has the same relative numbers and kinds of atoms. (numbers and kinds of atoms. (ProustProust))

Michael Faraday - 1839Michael Faraday - 1839

Suggested there was a connection between Suggested there was a connection between the structure of the atom and electricity. the structure of the atom and electricity.

E. Goldstein - 1886E. Goldstein - 1886

Isolated the Isolated the protonproton..

J.J. Thomson - 1896J.J. Thomson - 1896

Isolated the Isolated the electronelectron. . (cathode tube in the (cathode tube in the journal)journal)

Henri Becquerel - 1896Henri Becquerel - 1896

Accidentally discovered that uranium gave off Accidentally discovered that uranium gave off invisible rays. invisible rays. Photo plates were developed Photo plates were developed when put close to the sample of uranium. when put close to the sample of uranium. (journals)(journals)

Marie and Pierre Curie - 1898Marie and Pierre Curie - 1898

1.1. Named Becquerel’s invisible rays Named Becquerel’s invisible rays ““radiationradiation”.”.

2.2. Isolated the radioactive elements Isolated the radioactive elements poloniumpolonium and and radiumradium..

Ernest Rutherford - 1909Ernest Rutherford - 1909

1.1. Isolated Isolated alphaalpha and and beta radiationbeta radiation..

2.2. Found all of the atom’s protons were in the Found all of the atom’s protons were in the center of the atom and called this the center of the atom and called this the nucleusnucleus. . (gold foil experiment in journal) (gold foil experiment in journal)

Robert Millikan - 1909Robert Millikan - 1909

Found the mass (grams) and the charge Found the mass (grams) and the charge (columbs) of the electron. (columbs) of the electron. (Famous oil drop (Famous oil drop experiment done at he University of experiment done at he University of Chicago.)Chicago.)

Niels Bohr - 1911Niels Bohr - 1911

Proved electrons were in energy levels around Proved electrons were in energy levels around the nucleus. the nucleus. (The current model changes (The current model changes part of Bohr’s idea.)part of Bohr’s idea.)

James Chadwick - 1932James Chadwick - 1932

Found the nucleus of the atom also contained Found the nucleus of the atom also contained neutral particles; he called them neutral particles; he called them neutronsneutrons..