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350
Aristotle
350 BC – Aristotle disbelieved the ancient Greek theory of atoms being of different sizes, regular geometric shapes and being in constant motion. He didn't think atoms could be in constant motion in a void. He developed the theory that all matter consisted of four elements: Earth, Air, Water and Fire. There were also four qualities: dryness, hotness, coldness, and moistness. Fire was dry and hot; water was moist and cold, etc. His theory was used for almost 2000 years. -
442
Democritus
- "by convention bitter, by convention sweet, but in reality atoms and void.” Democritus was a Greek philosopher who developed the atomic theory of the universe. His atomic theory anticipated the modern principles of the conservation of energy and the irreducibility of matter.
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Antione Lavoisier
He found and termed both oxygen (1778) and hydrogen (1783), helped construct the metric system, put together the first extensive list of elements, and helped to reform chemical nomenclature. He was also the first to establish that sulfur was an element (1777) rather than a compound. He discovered that, although matter may change its form or shape, its mass always remains the same. Lavoisier could not entirely escape from Aristotle’s influence. The second element in his list is Aristotle’s “fire" -
John Dalton
Was a British chemist and physicist, who developed the atomic theory upon which modern physical science is founded. Dalton's most important contribution to science was his theory that matter is composed of atoms of differing weights and combine in simple ratios by weight. Proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass. -
Henri Becquerel
In 1896 while studying the effect of x-rays on photographic film, he discovered some chemicals spontaneously decompose and give off very penetrating rays. He discovered radioactivity. It happened by accident when he was investigating phosphorescence. Radioactivity demonstrated that the atom was neither indivisible nor immutable. For his discovery of spontaneous radioactivity Becquerel was awarded half of the Nobel Prize for Physics in 1903 along with Marie and Pierre Curie. -
Marie & Pierre Curie
Marie & Pierre Curie Studied uranium and thorium and called their spontaneous decay process "radioactivity". She and her husband Pierre also discovered the radioactive elements polonium and radium. Her achievements include the creation of a theory of radioactivity (a term coined by her) and the discovery of two new elements, radium and polonium. It was also under her personal direction that the world’s first studies were conducted into the treatment of cancers, using radioactive isotopes. -
J. J. Thompson
He was a British physicist and Nobel laureate. He is credited for the discovery of the electron and of isotopes, and the invention of the mass spectrometer. Thomson was awarded the 1906 Nobel Prize in Physics for the discovery of the electron and for his work on the conduction of electricity in gases. He was influenced by the work of James Clerk Maxwell. -
Max Planck
Was a German physicist, who is considered to be the founder of quantum theory, and one of the most important physicists of the twentieth century. This theory revolutionized our understanding of atomic and subatomic processes. He used the idea of quanta (discrete units of energy) to explain hot glowing matter. -
Robert Millikan
As an American physicist, Millikan made numerous important discoveries, chiefly in the fields of electricity, optics, and molecular physics. His earliest major success was the accurate determination of the charge carried by an electron, using the elegant "falling-drop method"; he also proved that this quantity was a constant for all electrons (1910), demonstrating the atomic structure of electricity. -
Ernest Rutherford
Ernest Rutherford was a British physicist, one of the most creative researchers in atomic physics. He discovered the transmutation of elements that is elements are not immutable, they can change their structure naturally by changing from heavy elements to slightly lighter elements. He was first to split the atom, he converted nitrogen into oxygen. He set forth the laws of radioactive decay. He identified alpha particles as helium nuclei. Rutherford proposed the nuclear model of the atom. -
Henry Mosely
Was a British chemist who studied under Rutherford and brilliantly developed the application of X-ray spectra to study atomic structure; Moseley's discoveries resulted in a more accurate positioning of elements in the Periodic Table by closer determination of atomic numbers. Moseley's law advanced atomic physics by providing the first experimental evidence in favor of Niels Bohr’s theory. -
Neils Bohr
Was 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’s work helped solve the problems classical physics could not explain about the nuclear model of the atom. He postulated that electrons moved in fixed orbits around the atom’s nucleus, and he explained how they emitted or absorbed energy. -
Werner Heisneberg
Heisenberg will always be associated with his theory of quantum mechanics, published in 1925, when he was 23 years old. For this theory and the applications of it which resulted especially in the discovery of allotropic forms of hydrogen, Heisenberg was awarded the Nobel Prize for Physics for 1932. -
Erwin Schrodinger
He laid the foundation of the wave-mechanics approach to quantum theory and set forth his now-famous wave equation. He succeeded (1927) Max Planck in the chair of theoretical physics. -
James Chadwick
Was a British physicist James Chadwick measured the energy of protons emerging from the hydrogen atoms. In 1932, Chadwick made a fundamental discovery in the domain of nuclear science: he proved the existence of neutrons - elementary particles devoid of any electrical charge
