History of the Atom

Democritus

460 BCE

Born around 460 BCE
Lived in Greece
Proposed the theory that matter was made up of little particles called atoms
Most didn’t believe his theory
Aristotle was his rival

John Dalton

1766

Lived from 1766-1844
Lived in England
Proposed that matter is composed of tiny particles called atoms
All atoms of the same element are identical but are different from the other elements atoms
Chemical reactions rearrange the atoms in whole number ratios
Was a meteorologist and would keep track of the weather daily
Used an arbitrary system to figure out the atomic structure of a compound

J.J. Thomson

1856

Lived from 1856-1940
Lived in the U.K.
“Plum Pudding” model
Atoms consist of a large sphere of positive charges with smaller negatively charged particles (corpuscles)
Total positive charge of sphere = total negative charge of the corpuscles
Was a professor of physics at Cambridge
His techniques let him develop the mass spectrograph

Marie Curie

1867

Lived from 1867-1934
Lived in Poland most of her life but lived in Paris for some time
Discovered radioactivity
Tested several substances and and performed many chemical reactions
Tests resulted in discovery of polonium and radium
Worked with her husband Pierre until his death in 1906
Was the first person to receive two Nobel Prizes; one in 1903 and one in 1911

Robert Millikan

1868

Lived from 1868-1953
Lived in Illinois
Conducted an experiment that allowed the value of the negative charge of the electron to be calculated
Conducted the oil drop experiment
Applied electrical force upward that matched the gravitational force downward, which caused the drops to be suspended
Developed qE=mg equation and the 1.60 x 10^-19 coulombs, which caused the charge on the electron to be found

Albert Einstein

1879

Lived from 1879-1955
Born in Germany but moved to Italy
Published five papers on physics
Developed a mathematical formula to explain that the visible motion of the particles was caused by the invisible motion of the molecules in the liquid
Received the Nobel Prize for this paper
The special theory of relativity was also developed (E= mc^2)
Wrote the general theory of relativity in 1915
After he died in 1955, the 99th element was discovered and named einsteinium

Niels Bohr

1885

Lived from 1885-1962
Lived in Copenhagen, Denmark
Proposed elections existed at set levels of energy
If atoms absorbed energy, the electron would jump to a level further from the nucleus
If it radiated energy, the electron went to a closer level of the nucleus
He offered a place where Jewish escapists and scientists could work during WWII
Worked on the atomic bomb at Los Alamos
Organized the Atoms for Peace Conference in Geneva in 1955
Helped found CERN
Died of a stroke in 1962

James Chadwick

1891

Lived from 1891-1974
Lived in the U.K.
The nucleus of an atom contain neutrons
Experimented with beryllium, helium, nitrogen, and lithium
Experiments determined the mass of the particle was greater than the mas
Was awarded the Nobel Prize for his discovery in 1935
Worked on the Manhattan Project

Louis De Broglie

1892

Lived from 1892-1987
Lived in France
Interested in the study of quanta
Researched the quantum theory
Developed the theory of wave mechanics
Studied the theory of light and other theories
Was awarded the Henri Poincaré medal in 1929 and the Albert I of Monaco prize in 1923

Werner Heisenberg

1901

Lived from 1901-1976
Lived in Bavaria and Munich
Realized the limitations of visual models and worked strictly with experimental data and mathematical results
Used mathematical physics with atomic physics called matrix mechanics
Realized the act of measuring an electron’s properties by hitting the electron with gamma rays would alter its behavior
Called it the uncertainty principle
Captured by the Allies after the war and was imprisoned for six months in England
Died in 1976