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Name: James Chadwick
Birth-Death: 20 October 1891 – 24 July 1974
Country of Origin: Bollington, Cheshire
Year of Discovery: discovered the neutron in 1932
Biography: James Chadwick was the son of John Joseph Chadwick and Anne Mary Knowles.
He attended Manchester High School prior to entering Manchester University in 1908. He
graduated from the Honours School of Physics in 1911 and spent the next two years under
Professor Rutherford in the Physical Laboratory in Manchester, where he worked on various
radioactivity problems, gaining his M.Sc. degree in 1913. That same year he was awarded the
1851 Exhibition Scholarship and proceeded to Berlin to work in the Physikalisch Technische
Reichsanstalt at Charlottenburg. He was in Germany at the start of World War I and was interned
in Ruhleben P.O.W. Camp just outside Berlin. During his internship he had the freedom to set up
a laboratory in the stables. With the help of Charles Ellis, he worked on the ionization of
phosphorus and also on the photo-chemical reaction of carbon monoxide and magnesium. He
spent most of the war years in Ruhleben until Geiger's laboratory requested for his release.
Discovery: In 1932, Chadwick discovered a previously unknown
particle in the atomic nucleus. This particle became known as the
neutron because of its lack of electric charge. Chadwick's discovery
was crucial for the fission of uranium 235. Unlike positively charged
alpha particles, which are repelled by the electrical forces present in
the nuclei of other atoms, neutrons do not need to overcome any
Coulomb barrier and can therefore penetrate and split the nuclei of
even the heaviest elements. For this discovery he was awarded the
Hughes Medal of the Royal Society in 1932 and the Nobel Prize for
Physics in 1935. Chadwick’s discovery made it possible to create
elements heavier than uranium in the laboratory. His discovery
particularly inspired Enrico Fermi, Italian physicist and Nobel laureate, to discover nuclear
reactions brought by slowed neutrons, and led Otto Hahn and Fritz Strassmann, German
radiochemists in Berlin, to the revolutionary discovery of “nuclear fission”.
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Name: Democritus
Birth-Death: (ca. 460 BCE – ca. 370 BCE)
Country of Origin: Abdera in the north of Greece
Biography: Democritus was born in the city of Abdera in Thrace, an Ionian colony of Teos,
although some called him a Milesian. Democritus spent the inheritance which his father left him
on travels into distant countries, to satisfy his thirst for knowledge. After returning to his native
land he occupied himself with natural philosophy. He travelled throughout Greece to acquire a
knowledge of its culture. He mentions many Greek philosophers in his writings, and his wealth
enabled him to purchase their writings. Leucippus, the
founder of the atomism, was the greatest influence upon
him. The many anecdotes about Democritus, demonstrate
his modesty, and simplicity, and show that he lived
exclusively for his studies.
Discovery: The hypothesis of Leucippus and Democritus
held everything to be composed of atoms, which are
physically, but not geometrically, indivisible. That between
atoms lies empty space; that atoms are indestructible; have
always been, and always will be, in motion. That, there are
an infinite number of atoms, and kinds of atoms, which
differ in shape, size, and temperature. Of the weight of atoms, Democritus said "The more any
indivisible exceeds, the heavier it is." But their exact position on weight of atoms is disputed.
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Name: Leucippus
Birth-Death: first half of 5th century BC
Country of Origin: Miletus or Abdera or Greece
Biography: Leucippus was a shadowy figure, as his dates
are not recorded and he is often mentioned in conjunction
with his more well-known pupil Democritus. It is therefore
difficult to determine which contributions come from
Democritus or from those of Leucippus. Leucippus was a
contemporary of Zeno, Empedocles and Anaxagoras of the
Ionian school of philosophy.
Discovery: Leucippus was the first Greek to develop the
theory of atomism: the idea that everything is composed
entirely of various imperishable, indivisible elements called
atoms. This was elaborated in far greater detail by his
student and successor, Democritus. His discoveries impacted the development of atoms because
he was the original founder, and influenced Democritus in order to keep investigating his theory.
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Name: Robert Millikan
Birth-Death: (22 March 1868 – 19 December 1953)
Country of Origin: American
Year of Discovery: Starting in 1909- published his seminal study in 1913
Biography: Millikan went to high school in Maquoketa, Iowa. Millikan received a Bachelor's
degree in the classics from Oberlin College in 1891 and his doctorate in physics from Columbia
University in 1895. He was the first to earn a Ph.D. from that department. Millikan's enthusiasm
for education continued throughout his career, and he was the coauthor of a popular and
influential series of introductory textbooks, which were ahead of their time in many ways.
Compared to other books of the time, they treated the subject more in the way in which it was
thought about by physicists. They also included many homework problems that asked conceptual
questions, rather than simply requiring the student to plug numbers into a formula. In 1902 he
married Greta Ervin Blanchard. They had three sons: Clark Blanchard, Glenn Allen, and Max
Franklin
Discovery: Starting in 1909, while a professor at the University of Chicago, Millikan and
Harvey Fletcher worked on an oil-drop experiment, in which
they measured the charge on a single electron. Professor
Millikan took individual credit, in return for Fletcher claiming
full authorship on a related result for his study. Millikan went on
to win the 1923 Nobel Prize for Physics, in part for this work,
and Fletcher kept the agreement a secret until his death. After a
publication on his first results in 1910, contradictory
observations by Felix Ehrenhaft started a controversy between
the two physicists. After improving his setup he published his
seminal study in 1913. The elementary charge is one of the
fundamental physical constants and accurate knowledge and its
value is of great importance. His experiment measured the force
on tiny charged droplets of oil suspended against gravity
between two metal electrodes.
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Name: Erwin Schrödinger
Birth-Death: 12 August, 1887, Erdberg – 4 January, 1961, Vienna
Country of Origin: Austrian
Biography: In 1887 Schrödinger was born in Vienna, Austria to Rudolf Schrödinger and
Georgine Emilia Brenda. In 1898 he attended the Akademisches Gymnasium. Between 1906 and
1910 Schrödinger studied in Vienna under Franz Serafin Exner (1849 - 1926) and Friedrich
Hasenöhrl (1874 - 1915). He also conducted experimental work with K.W.F. Kohlrausch. In
1911, Schrödinger became an assistant to Exner. At an early age, Schrödinger was strongly
influenced by Schopenhauer. As a result of his extensive reading of Schopenhauer's works, he
became deeply interested throughout his life in color theory, philosophy, perception, and eastern
religion, especially Vedanta.
Discovery: Schrödinger's wave equation was based on the Heisenberg uncertainty principal that
the position and velocity of an electron cannot be determined accurately. Schrödinger's wave
equation gave a wave function, which squared gave the probability cloud of electrons. Therefore,
Schrödinger's contribution resulted in the electron cloud model of the atom. Erwin Schrodinger
added the final piece to the puzzle of electron
arrangement around the nuclei of atoms. He
suggested that electrons behave in a wave-like
manner rather than just as particles and that their
exact location within an orbit could not be precisely
calculated. This impacted the model of the atom
deeply, since the movement of the electrons was
changed.
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Name: Marie Curie
Birth-Death: November 7, 1867 – July 4, 1934
Country of Origin: Polish
Biography: She was a pioneer in the field of
radioactivity, the first person honored with two Nobel
Prizes, and the first female professor at the University of
Paris She was born Maria Skłodowska in Warsaw and
lived there until she was 24. In 1891 she followed her
elder sister Bronisława to study in Paris, where she
obtained her higher degrees and conducted her subsequent scientific work. She founded the
Curie Institutes in Paris and Warsaw. Her husband Pierre Curie was a Nobel co-laureate of hers,
and her daughter Irène Joliot-Curie and son-in-law Frédéric Joliot-Curie also received Nobel
prizes.
Discovery: Marie and Pierre Curie’s work in radioactivity revolutionized science in the late 19th
Century. Marie Curie’s hypothesis that radiation was “an atomic property” transformed forever
how man would view the atom. There are some biographers who have said that this, and only
this, was Marie Curie’s great discovery.
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Name: Werner Heisenberg
Birth-Death: 5 December 1901 – 1 February 1976
Country of Origin: German
Biography: Heisenberg was born in Würzburg, Germany to Kaspar
Ernst August Heisenberg, He studied physics and mathematics from
1920 to 1923 at the Ludwig-Maximilians-Universität München and
the Georg-August-Universität Göttingen. At Munich, he studied
under Arnold Sommerfeld and Wilhelm Wien. At Göttingen, he
studied physics with Max Born and James Franck, and he studied
mathematics with David Hilbert. He received his doctorate in 1923,
at Munich under Sommerfeld. He completed his Habilitation in
1924, at Göttingen under Born. Because Sommerfeld had a sincere
interest in his students and knew of Heisenberg's interest in Niels
Bohr's theories on atomic physics, Sommerfeld took Heisenberg to
Göttingen to the Bohr Festival in June 1922. At the event, Bohr was
a guest lecturer and gave a series of comprehensive lectures on
quantum atomic physics. There, Heisenberg met Bohr for the first
time, and it had a significant and continuing effect on him.
Discovery: Heisenberg suggested that any theory of the atom must be based on observable
phenomenon, such as the spectral lines emitted by atoms, and not pictorial constructs such as
Bohr's nuclear model of the atom. For Heisenberg, this observable data could be culled to
formulate a set of possible values for a hypothetical particle. These values could then be used to
calculate, by mean of mathematical formulas, the probabilities of particular energy states and
transitions among those states.
Dalton's model was that the atoms were tiny, indivisible, indestructible particles and that each
one had a certain mass, size, and chemical behavior that was determined by what kind of element
they were.
The plum pudding model of the atom by J. J. Thomson, who discovered the electron in 1897,
was proposed in 1904 before the discovery of the atomic nucleus. In this model, the atom is
composed of electrons surrounded by a soup of positive charge to balance the electron's negative
charge, like negatively-charged "plums" surrounded by positively-charged "pudding". The
electrons were thought to be positioned throughout the atom, but with many structures possible
for positioning multiple electrons, particularly rotating rings of electrons . Instead of a soup, the
atom was also sometimes said to have had a cloud of positive charge.
The Rutherford–Bohr model of the hydrogen
atom (Z = 1) or a hydrogen-like ion (Z > 1), where the negatively charged electron confined to
an atomic shell encircles a small, positively charged atomic nucleus and where an electron jump
between orbits is accompanied by an emitted or absorbed amount of electromagnetic energy (hν).
The orbits in which the electron may travel are shown as grey circles; their radius increases as n2,
where n is the principal quantum number. The 3 → 2 transition depicted here produces the first
line of the Balmer series, and for hydrogen (Z = 1) it results in a photon of wavelength 656 nm
(red light).
In atomic physics, the Bohr model, devised by Niels Bohr, depicts the atom as a small, positively
charged nucleus surrounded by electrons that travel in circular orbits around the nucleus, similar
in structure to the solar system, but with electrostatic forces providing attraction, rather than
gravity. This was an improvement on the earlier cubic model (1902), the plum-pudding model
(1904), the Saturnian model (1904), and the Rutherford model (1911). Since the Bohr model is a
quantum physics-based modification of the Rutherford model, many sources combine the two,
referring to the Rutherford–Bohr model.