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465 BCE
Democritus
Country of Orgin - Greek
Date of Discovery- 465 B.C.
Theory development- His atomic theory stated that “The universe is composed of two elements: the atoms and the void in which they exist and move.” Democritus thought that atoms were miniscule quantities of matter. Democritus hypothesized that atoms cannot be destroyed, differ in size, shape and temperature, are always moving, and are invisible. He believed that there are an infinite number of atoms. -
John Dalton
Country of Orgin- Eaglesfield,UK
Date of Discovery- 1803
Dalton's atomic theory consisted of 4 steps:
1) All matter is made of atoms. Atoms are indivisible and indestructible.
2) All atoms of a given element are identical in mass and properties
3) Compounds are formed by a combination of two or more different kinds of atoms.
4) A chemical reaction is a rearrangement of atoms.
Dalton introduced his belief that atoms of different elements could be determined based on their atomic weight. -
JJ Thomson
Country of origin- Cheetham Hill, Manchester England
Date of Discovery- 1897
Theory development- discovered electrons and noticed that an atom can be divided. He also said atoms are made of positive cores and negatively charged particles within it. He developed the Plum Pudding Model before the atomic nucleus was discovered. This model shows that the electrons are surrounded by a "pudding" of positive charges to balance the negative charges. -
Ernest Rutherford
Country of origin- Spring Grove, United Kingdom
Date of discovery- 1898
Theory development- Rutherford made the discovery that nearly the total mass of an atom is concentrated in a nucleus. In so doing, he gave birth to the nuclear model, a discovery that marked the inception of nuclear physics and ultimately paved the way to the invention of the atom bomb. -
Robert Millikan
Country of Origin- Morrison Illinois, United States of America
Date of Discovery- 1910
Atomic Theory development - accurately determining the charge carried by an electron, using the elegant "falling-drop method". This method consisted of dropping small globules of oil over a magnet into the path of an x-ray. When the x-ray particles made contact with the oil, the charge would change causing the oil to fall slower, stay still, or even start rising. -
Niels Bohr
Country of Orgin- Copenhagen, Denmark
Date of Discovery- 1913
Niels Bohr proposed a theory for the hydrogen atom based on quantum theory that energy is transferred only in certain well defined quantities. Electrons should move around the nucleus but only in prescribed orbits. When jumping from one orbit to another with lower energy, a light quantum is emitted. Bohr's theory could explain why atoms emitted light in fixed wavelengths. -
Louis de Brogile
Date of Discovery- 1923
Country of Origin- Dieepe, France
Theory development- His ideas were a basis for developing the wave mechanics theory. This theory has greatly improved our knowledge of the physical nature on the atomic scale.He believed that electrons can act like both particles and waves, just like light. He also said that waves produced by electrons contained in the orbit around the nucleus, set up a standing wave of a certain energy, frequency, and wavelength. -
Erwin Schrodinger
Country of Origin- Vienna Austria
Date of discovery- 1930
Theory development- Following the atomic model of Niels Bohr and a thesis from de Broglie, Schrödinger articulated the movements of electrons in terms of wave mechanics as opposed to particle leaps. He provided a mode of thought to scientists that would become accepted and incorporated into thousands of papers, thus becoming an important cornerstone of quantum theory. -
James Chadwick
Date of discovery- 1932
Country of origin- Chesire, England
Theory development- Chadwick is best known for his discovery of the neutron in 1932. Bombarding elements with neutrons can succeed in penetrating and splitting nuclei, generating an enormous amount of energy. Chadwick's findings were pivotal to the discovery of nuclear fission, and ultimately the development of the atomic bomb.
