History of Atomic Theory

Democritus

460 BCE

(460- 370 BC) Abdera, Greece
-Developed the idea that everything is made up of atoms and a void in which they move in. Concluding that they are indestructible and in constant movement
-His model consists of a single sphere demonstrating an atom
-Made his discovery out of thought when being taught by his teacher Leucippus
-Considered "Father of Modern Science" after his discovery
(https://www.iep.utm.edu/democrit/)

John Dalton

1803

(1766-1844)Eaglesfield, United Kingdom
1.States that all matter is composed of atoms that are invisible, indestructible building blocks
2.All the atoms of a given element are the same in mass and properties
3.Compounds are formed with two or more different kinds of atoms.
4.Rearranging of atoms is a chemical reaction
5.Atoms of one element are unique
-Discovered his theory while experimenting with gases
-Taught mathematics & natural philosophy
(https://www.britannica.com/biography/John-Dalton)

J.J Thomson

1897

(1856-1940)Cheetham Hill, Manchester
Determined that all matter is made up tiny particles that are much smaller than atoms that are now called electrons, prevailing the theory that an atom is the smallest fundamental unit.
Cathode Ray Experiment, ¨Plum Pudding model¨
-Discovered that neon is composed of two different type of atoms while also proving the existence of isotopes.
(http://www.abcte.org/files/previews/chemistry/s1_p5.html)

Cathode Ray Experiment

1897

-Thomson used a negative plate on one side of the tube and a positive plate on the other which created a magnet that bent the cathode rays away from the electrometers. In doing so, he discovered that the electrometers stopped measuring electric charge. From this he hypothesized that the electric charge and the cathode rays must be combined together and not separate entities.

Robert Millikan

1909

(1868-1953)Morrison, Illinois
Determined the unit charge of an electron
Oil drop experiment
Fact- During the Second World War he worked for the military with things of aeronautics and meteorology.
(https://www.nobelprize.org/prizes/physics/1923/millikan/biographical/)
(http://ffden-2.phys.uaf.edu/212_fall2003.web.dir/Ryan_McAllister/Slide3.htm)

Oil Drop Experiment

1909

-As the oil is sprayed the droplets fall through the hole to the next chamber where the air is ionized by x-rays. The batteries attached to the plates applies an electric voltage, creating an electric field. With the correct amount of voltage the electromagnetic force will balance with gravity, causing the drop of oil to “float”. This allowed Millikan to determine the charge of an electron.

Earnest Rutherford

1911

(1871-1937)Brightwater New Zealand
Discovered that an atom has a nucleus
Model is called the Rutherford model (planetary model)
Gold Foil experiment
http://www.iun.edu/~cpanhd/C101webnotes/modern-atomic-theory/rutherford-model.html

Gold Foil Experiment

1911

-He came to this discovery by shooting particles at a piece of gold foil, most going through like expected but some bouncing back. He hypothesized that the only explanation was that the mass was concentrated into a nucleus. Fact- His research in conducting a reaction between nitrogen and alpha particles led to the discovery of splitting atoms

Neils Bohr

1913

(1885-1962) Copenhagen, Denmark
-Bohr discovers that the atom contains electrons that travel in separate orbits while also finding that the total amount of electrons in the outer orbit equals to the properties of an element
-He made his theory based on the quantum theory (planetary model)
-Bhor and Einstein were close friends that had many conversations over physics.
http://mentalfloss.com/article/544594/facts-about-physicist-niels-bohr

Erwin Schrodinger

1926

(1887-1961) Erdberg, Vienna, Austria

-Created results in the field of quantum theory which helped him formulate the wave equation. This formula calculated the certain position of an electron.
-He was an only child with the father of Rudolf Schrödinger and married to Annemarie Betel.
(https://www.nobelprize.org/prizes/physics/1933/schrodinger/biographical/)

James Chadwick

1932

(1891-1974)Bollington, United Kingdom
-His was known for his discovery of neutron
Ruthford predicted of something else in the nucleus of an atom. Chadwick done a series of test that included beryllium in a vacuum chamber with some polonium. As the polonium produced alpha rays the beryllium then produced neutral rays.
-quantum mechanical model
-Chadwick's findings were vital to the discovery of nuclear fission (development of atomic bomb)
http://scienceline.ucsb.edu/getkey.php?key=1