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460
Democritus
According to ancient reports, Democritus was born about 460 BCE (thus, he was a younger contemporary of Socrates) and was a citizen of Abdera, although some reports mention Miletus. As well as his associate or teacher Leucippus, Democritus is said to have known Anaxagoras, and to have been forty years younger than the latter (DK 68A1). A number of anecdotes concern his life, but their authenticity is uncertain. Called the particles of matter atoms. -
John Dalton
He proposed an atomic theory with spericail solid masses in motion. Dalton also came to believe that the particles in different gases had different volumes and surrounds of caloric, thus explaining why a mixture of gases—as in the atmosphere—would not simply layer out but was kept in constant motion. Dalton consolidated his theories in his New System of Chemical Philosophy (1808–1827). -
JJ Thomson
Thomson went to America in 1904 to deliver six lectures on electricity and matter at Yale University. They contained some important suggestions as to the structure of the atom. He discovered a method for separating different kinds of atoms and molecules by the use of positive rays, an idea developed by Aston, Dempster and others towards the discovery of many isotopes. He aslo discovered the electron, -
Ernest Rutherford
A New Zealand chemist and physicist who became known as the father of nuclear physics. He discovered that atoms have a small charged nucleus, and there by pioneered the Rutherford model of the atom, through his discovery of Rutherford scattering with his gold foil experiment. He is widely credited as splitting the atom in 1917 and leading the first experiment he found the necleous of the atom is dense and has a positive charge. -
Neils Bohr
A Danish physicist who made fundamental contributions to understanding atomic structure and quantum mechanics, for which he received the Nobel Prize in Physics in 1922. Bohr mentored and collaborated with many of the top physicists of the century at his institute in Copenhagen. He was also part of the team of physicists working on the Manhattan Project. He also found that the atomic structure of the atom as "successive orbital shells of electrons". -
De Broglie and Schodinger
Identified the electron cloud model as the propable location of moving electron. -
James Chadwick
Discovered a particle within the nucleus that has a mass similat to that of a proton. He also discovered the nutron -
James Chadwick
Chadwick made a fundamental discovery in the domain of nuclear science: he proved the existence of neutrons - elementary particles devoid of any electrical charge. In contrast with the helium nuclei (alpha rays) which are charged, and therefore repelled by the considerable electrical forces present in the nuclei of heavy atoms, this new tool in atomic disintegration need not overcome any electric barrier and is capable of penetrating and splitting the nuclei of even the heaviest elements. -
Bombing of Hiroshima and Nagasaki
The atomic bombings of Hiroshima and Nagasaki were nuclear attacks near the end of World War II against the Empire of Japan by the United States at the executive order of U.S. President Harry S. Truman on August 6 and August 9, 1945, respectively. After six months of intense fire-bombing of 67 other Japanese cities, followed by an ultimatum which was ignored by the Shōwa regime, the nuclear weapon "Little Boy" was dropped on the city of Hiroshima on Monday, August 6, 1945, and August 9, 1945
