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Russell Metcalfe
Jonathon Emond
Atomic
History
Timeline
Democritus
Democritus was born in Abdera, the leading Greek city on the northern coast of the
Aegean Sea, in the year 460 BC. Although the ancient accounts of Democritus's career
differ widely, they all agree that he lived to a ripe old age, 90 being the lowest figure.
Therefore this would put his death around 370 BC. Democritus agreed that everything
which is must be eternal, but denied that "the void" can be equated with nothing. This
makes him the first thinker on record to argue the existence of an entirely empty "void".
In order to explain the change around us from basic, unchangeable substance he
created a theory that argued that there are various basic elements which always existed
but can be rearranged into many different forms. Democritus' theory argued that atoms
only had several properties, particularly size, shape, and (perhaps) weight; all other
properties that we attribute to matter, such as color and taste, are but the result of
complex interactions between the atoms in our bodies and the atoms of the matter that
we are examining. Furthermore, he believed that the real properties of atoms determine
the perceived properties of matter--for example, something that is solid is made of
small, pointy atoms, while something that has water like properties is made of large,
round atoms. Some types of matter are particularly solid because their atoms have
hooks to attach to each other; some are oily because they are made of very fine, small
atoms which can easily slip past each other. In Democritus' own words: By convention
there is sweet, by convention there is bitterness, by convention hot and cold, by
convention color; but in reality there are only atoms and the void.
http://www.bookrags.com/biography/democritus/
http://en.wikipedia.org/wiki/Democritus
John
Dalton
John Dalton (1766–1844) was born into a modest Quaker family in Cumberland,
England, and earned his living for most of his life as a teacher and public lecturer,
beginning in his village school at the age of 12. After teaching 10 years at a Quaker
boarding school in Kendal, he moved on to a teaching position in the burgeoning city of
Manchester. There he joined the Manchester Literary and Philosophical Society, which
provided him with a stimulating intellectual environment and laboratory facilities. The
first paper he delivered before the society was on color blindness, which afflicted him
and is sometimes still called "Daltonism."He proceeded to calculate atomic weights from
percentage compositions of compounds, using an arbitrary system to determine the
likely atomic structure of each compound. If there are two elements that can combine,
their combinations will occur in a set sequence. The first compound will have one atom
of A and one of B; the next, one atom of A and two atoms of B; the next, two atoms of A
and one of B; and so on. Hence, water is HO. 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).
http://www.chemheritage.org/classroom/chemach/periodic/dalton.html
Marie
Curie
Marie Sklodowska Curie (1867–1934) was the first person ever to receive two Nobel
prizes: the first in 1903 in physics, shared with her husband Pierre and Henri Becquerel
for the discovery of the phenomenon of radioactivity; and the second in 1911 in
chemistry for the discovery of the radioactive elements polonium and radium. The
daughter of impoverished Polish schoolteachers, Marie worked as a governess in
Poland to support her older sister in Paris, whom she eventually joined. Already
entranced with chemistry, Marie took advanced scientific degrees at the Sorbonne,
where she met and married Pierre Curie, a physicist who had achieved fame for his
work on the piezoelectric effect. For her thesis she chose to work in a field just opened
up by Wilhelm Roentgen's discovery of X-rays and Becquerel's observation of the
mysterious power of samples of uranium salts to expose photographic film. She soon
convinced her husband to join in the endeavor of isolating the "radioactive" substance—
a word she coined. In 1898, after laboriously isolating various substances by successive
chemical reactions and crystallizations of the products, which they then tested for their
ability to ionize air, the Curies announced the discovery of polonium, and then of radium
salts weighing about 0.1 gram that had been derived from tons of uranium ore.
http://www.chemheritage.org/classroom/chemach/atomic/curie.html
W.K. Roentgen was born in 1845 from a wealthy family of dealers in the small city of
Lennep, in north-western Germany; after having spent the most greater part of the
infancy in the Low Countries, to the twenty year-old age he transferred later to Zurich
and three years he/she graduated him in engineering near the Technische Hochschule.
Although you/he/she had not followed some course of experimental physics during the
studies, definite to develop searches in this sector after the diploma.
After having received the doctorate in 1869, Roentgen got a series of charges as
teacher in various German universities and in collaboration with Kundt it performed
careful studies on the behavior of the subject; for example it was the first one to show,
with a thermometer done in house, that is easier to heat the damp air that the dry air.
Roentgen had quarantatré years when it became teacher of physics and manager of the
institute of Physics of the university of Wurzburg, a prosperous Bavarian town; he/she
lived with his/her wife Bertha in an ample apartment to the second floor of the institute
that understood a communicating study with a private laboratory. In June 1894 it started
to study the cathode rays, to that time matter of very popular search and the night of
November 8 th 1895 during one of his/her experiments it reached the discovery of a
type of rays of unknown nature that called "X rays."
Three weeks later spread Roentgen the news of his/her discovery: the fact to be able to
see through the objects without breaking them and inside the human body aroused
great sensation. In consequence of this he acquired a great fame and in 1901
you/he/she was assigned him the first Nobel prize for the physics
Roentgen died in 1923.
http://www.akisrx.com/inglese/htm/roentgen.htm
JJ Thomson
In 1897 the physicist Joseph John (J. J.) Thomson (1856–1940) discovered the electron
in a series of experiments designed to study the nature of electric discharge in a highvacuum cathode-ray tube—an area being investigated by numerous scientists at the
time. Thomson interpreted the deflection of the rays by electrically charged plates and
magnets as evidence of "bodies much smaller than atoms" that he calculated as having
a very large value for the charge to mass ratio. Later he estimated the value of the
charge itself. In 1904 he suggested a model of the atom as a sphere of positive matter
in which electrons are positioned by electrostatic forces. His efforts to estimate the
number of electrons in an atom from measurements of the scattering of light, X, beta,
and gamma rays initiated the research trajectory along which his student Ernest
Rutherford moved. Thomson's last important experimental program focused on
determining the nature of positively charged particles. Here his techniques led to the
development of the mass spectroscope, an instrument perfected by his assistant,
Francis Aston, for which Aston received the Nobel Prize in 1922. 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
positivecharge.
http://www.chemheritage.org/classroom/chemach/atomic/thomson.html
http://en.wikipedia.org/wiki/Plum_pudding_model
Ernest
Rutherford
Ernest Rutherford was born in Brightwater, New Zealand, into a family of pioneer stock
who had emigrated from Britain less than 30 years earlier. Although he was a very good
all-round scholar while at school, Rutherford showed no real bias to science. In 1890 he
entered Canterbury College at Christchurch in New Zealand, where his scientific ability
became apparent, and graduated with first-class degrees in both science and
mathematics. Rutherford proposed that the atom contained a massive nucleus
containing all of its positive charge, and that the much lighter electrons were outside this
nucleus. The nucleus had a radius about ten thousand times smaller than the radius of
the atom, only ten femtometers, or one hundred thousand billionth of a meter.
Scattering at large angles occurred when the alpha particles came near to a nucleus.
The reason that most alpha particles were not scattered at all was that they were
passing through the relatively large 'gaps' between nuclei. Rutherford revised
Thomson's 'plum pudding' model, showing how electrons could orbit a positively
charged nucleus, like planets orbiting a sun. In 1915 Neils Bohr adapted Rutherford's
model by saying that the orbits of the electrons were quantized, meaning that they could
exist only at certain distances from the nucleus. The Rutherford model of the atom was
soon superseded by the Bohr model, which used some of the early quantum
mechanical results to give locational structure to the behavior of the orbiting electrons,
confining them to certain circular (and later elliptical) planar orbits. In the Bohr model,
expanding on the work of Henry Moseley, the central charge was identified as being
directly connected with the atomic number (that is, the element's place on the periodic
table). Since the Bohr model is an improvement on the Rutherford model in this and
other ways, some sources combine the two, referring to the Bohr model as the
Rutherford-Bohr model. However, even an atom with a core containing an atomic
number of charges was the work of a number of men, including those mentioned, and
also
lesser
known
workers
such
as
Antonius
Van
den
Broek.
The Rutherford model was important because it essentially proposed the concept of the
nucleus, although this word is not used in the paper. What Rutherford notes as the
(probable) concomitant of this results, is a "concentrated central charge" in the atom:
"Considering the evidence as a whole, it seems simplest to suppose that the atom
contains a central charge distributed through a very small volume, and that the large
single defluxions are due to the central charge as a whole, and not to its constituents."
The central charge containing most of the atom's positive charge, invariably later
become associated with a concrete structure, the atomic nucleus. After the Rutherford
model and its confirmation in the experiments of Henry Moseley and its theoretical
description in the Bohr model of the atom, the study of the atom branched into two
separate fields, nuclear physics, which studies the nucleus of the atom, and atomic
physics
which
studies
atom's
electronic
structure.
http://www.daviddarling.info/encyclopedia/R/Rutherford_Ernest.html
http://en.wikipedia.org/wiki/Rutherford_model
Robert
Millikan
Robert Andrews Millikan (March 22, 1868 – December 19, 1953) was an American
experimental physicist, and Nobel laureate in physics for his measurement of the
charge on the electron and for his work on the photoelectric effect. He served as
president
of
Caltech
from
1921
to
1945.
The purpose of Robert Millikan and Harvey Fletcher's oil-drop experiment (1909) was to
measure the electric charge of the electron. They did this by carefully balancing the
gravitational and electric forces on tiny charged droplets of oil suspended between two
metal electrodes. Knowing the electric field, the charge on the oil droplet could be
determined. Repeating the experiment for many droplets, they found that the values
measured were always multiples of the same number. They interpreted this as the
charge on a single electron: 1.602 × 10−19 coulomb (SI unit for electric charge).
http://en.wikipedia.org/wiki/Oil-drop_experiment
Henri
Becquerel
Antoine Henri Becquerel (15 December 1852 – 25 August 1908) was a French
physicist, Nobel laureate, and one of the discoverers of radioactivity. He won the 1903
Nobel
Prize
in
Physics
for
discovering
radioactivity
French physics Professor Antoine Henri Becquerel discovered that uranium compounds
produced rays that blacked photographic plates. Radioactivity or radioactive is the name
of the property possessed by some elements of spontaneously emitting energetic
particles and rays from their atomic nuclei. These emitted particles or rays are called
radiation. An elemental material (such as uranium) that emits radiation is called
radioactive material. Most, but not all, atomic nuclei are stable i.e. not radioactive.
Radioactivity is a naturally occurring process that occurs when an unstable nucleus
goes through a transformation, moving to a lower energy state accessible to the
nucleus. The nuclei apart releasing energy in order to become stable. Nature always
universally
prefers
to
seek
its
lowest
energy
state.
http://www.bccdc.org/content.php?item=67
Erwin
Schrodinger
Erwin Rudolf Josef Alexander Schrödinger (12 August 1887 – 4 January 1961) was an
Austrian theoretical physicist who achieved fame for his contributions to quantum
mechanics, especially the Schrödinger equation, for which he received the Nobel Prize
in 1933. In 1935, after extensive correspondence with personal friend Albert Einstein,
he
proposed
the
Schrödinger's
cat
thought
experiment.
http://en.wikipedia.org/wiki/Erwin_Schr%C3%B6dinge
Werner
Heisenberg
Werner Heisenberg (5 December 1901 in Würzburg–1 February 1976 in Munich) was a
German theoretical physicist, best known for enunciating the Kramers-Heisenberg
dispersion formula. He made important contributions to quantum mechanics, nuclear
physics,
quantum
field
theory,
and
particle
physics.
The Kramers-Heisenberg dispersion formula is an expression for the cross section for
scattering of a photon by an atomic electron. It was derived before the advent of
quantum mechanics by Hendrik Kramers and Werner Heisenberg in 1925, based on the
correspondence principle applied to the classical dispersion formula for light. The
quantum mechanical derivation was given by Paul Dirac in 1927.
The Kramers-Heisenberg formula was an important achievement when it was
published, explaining the notion of "negative absorption" (stimulated emission), the
Thomas-Reiche-Kuhn sum rule, and inelastic scattering - where the energy of the
scattered photon may be larger or smaller than that of the incident photon – thereby
anticipating
the
Raman
effect.
http://en.wikipedia.org/wiki/Kramers-Heisenberg_formula
Niels Henrik David Bohr was born in Copenhagen on October 7, 1885, as the son of
Christian Bohr, Professor of Physiology at Copenhagen University, and his wife Ellen,
née Adler. Niels, together with his younger brother Harald (the future Professor in
Mathematics), grew up in an atmosphere most favourable to the development of his
genius - his father was an eminent physiologist and was largely responsible for
awakening his interest in physics while still at school, his mother came from a family
distinguished
in
the
field
of
education.
After matriculation at the Gammelholm Grammar School in 1903, he entered
Copenhagen University where he came under the guidance of Professor C.
Christiansen, a profoundly original and highly endowed physicist, and took his Master's
degree
in
Physics
in
1909
and
his
Doctor's
degree
in
1911.
http://nobelprize.org/nobel_prizes/physics/laureates/1922/bohr-bio.html
James
Chadwick
James Chadwick discovered the neutron in 1932, resulting in the solution of the jig-saw
puzzle for the weight of atoms. His discovery formed the base for the investigation of
the tougher questions of nuclear physics: the nature of the nucleus and its forces. In
1935, he received the Nobel Prize for Physics. Chadwick was knighted in 1945, and
died
in
1974
at
Cambridge.
Chadwick was born in 1891 in Manchester, England. He was graduated from
Manchester University in 1911 and remained to work with Ernest Rutherford. In 1913,
he received a scholarship to study in German, placing him in Germany at the beginning
of World War I. After Chadwick was detained as a civilian prisoner of war, he returned to
England in 1919 to carry out research at Cambridge University. In 1923, he became the
assistant
director
of
research
at
the
Cavendish
Laboratory.
Rutherford discovered that atoms have minute and dense nuclei, with the nucleus
holding a positive charge in the charge of a hydrogen nucleus. Physicists wanted to
determine where the extra mass was living. Chadwick helped answer this question
when identifying the neutron (particle without an electric charge in the nucleus) in 1932.
Chadwick had created an experiment to answer the question of this unknown nucleus
mass
source.
Chadwick smashed alpha particles into beryllium, a rare metallic element, and allowed
the radiation that was released to hit another target: paraffin wax. When the beryllium
radiation hit hydrogen atoms in the wax, the atoms were sent into a detecting chamber.
In physics it is known that only a particle having almost the same mass as a hydrogen
atom could affect hydrogen in that manner. The experiment results showed a collision
with beryllium atoms would release massive neutral particles, which Chadwick named
neutrons.
This
provided
the
answer
for
hidden
mass
in
atoms.
Chadwick's discovery advanced experimental work for all scientists. Since neutrons
have no electrical charge, any neutrons fired from a source has the ability to go through
deep layers of materials and to go into the nuclei of the target atoms. After Chadwick's
work, scientists world-wide began bombardment of all types of materials with neutrons.
It was discovered that when uranium is a target, nuclear fission becomes possible,
resulting
in
nuclear
weapons
and
nuclear
power
plants.
In 1935, Chadwick received the Nobel Prize for Physics for this discovery. During World
War II, he worked with the British atomic bomb project, and was a science advisor to
Oppenheimer on the Manhattan Project. The Manhattan Project was the first time an
atomic bomb had been produced. Chadwick was knighted in 1945, and died in 1974 at
Cambridge.
W.K. Roentgen was born in 1845 from a wealthy family of dealers in the small city of
Lennep, in north-western Germany; after having spent the most greater part of the
infancy in the Low Countries, to the twenty year-old age he transferred later to Zurich
and three years he/she graduated him in engineering near the Technische
Hochschule. Although you/he/she had not followed some course of experimental
physics during the studies, definite to develop searches in this sector after the
diploma.
After having received the doctorate in 1869, Roentgen got a series of charges as
teacher in various German universities and in collaboration with Kundt it performed
careful studies on the behavior of the subject; for example it was the first one to show,
with a thermometer done in house, that is easier to heat the damp air that the dry air.
Roentgen had quarantatré years when it became teacher of physics and manager of
the institute of Physics of the university of Wurzburg, a prosperous Bavarian town;
he/she lived with his/her wife Bertha in an ample apartment to the second floor of the
institute that understood a communicating study with a private laboratory. In June
1894 it started to study the cathode rays, to that time matter of very popular search
and the night of November 8 th 1895 during one of his/her experiments it reached the
discovery of a type of rays of unknown nature that called "X rays."
Three weeks later spread Roentgen the news of his/her discovery: the fact to be able
to see through the objects without breaking them and inside the human body aroused
great sensation. In consequence of this he acquired a great fame and in 1901
you/he/she was assigned him the first Nobel prize for the physics
Roentgen died in 1923.
Electron cloud model
Electron Cloud Model
There are three important people that all contributed greatly to the discovery of
the electron cloud model. They are Ernest Rutherford, Neils Bohr, and Werner
Heisenberg. Rutherford brought to the table that the center of an atom had the positive
charge and mass were concentrated in the middle. Neils Bohr taking what Rutherford
had said came up with the theory that electrons are constricted to predetermined orbits
and can transition between orbits on absorbing or emitting energy. Werner Heisenberg
suggested that the only way to describe the location of an electron is through the
probability of distribution.
Heisenburg’s suggestion formed the basis of the electron cloud model. The
electron cloud model shows the most probable locations of electrons in an atom. Where
the cloud is denser is where you will most likely find an electron. The purpose of the
electron cloud model is to describe the location of electrons around the nucleus.
Rutherford-Bohr Model
The Rutherford-Bohr Model is the quantum model for the hydrogen atom.
Electrons in an H2 atom moves around the nucleus only in certain allowed circular
orbits. The model fits the quantized energy levels of the H2 atom and postulates only
certain circular orbits for the electron. When the electron becomes more tightly bound,
its energy becomes more positive.
Although this model was a great discovery, there were two limitations. The first
limitation was that the model is not applicable for any other atom except hydrogen. The
second limitation was that the model is fundamentally incorrect.
Atomic Planetary Model
Rutherford tested J.J. Thomson’s plum pudding model with the “gold foil”
experiment. He suggested that if Thomson was right the mass would spread throughout
the atom. So hypothetically if you shoot high velocity alpha particles at an atom there
should be very little to deflect the alpha particles. Some of the alpha particles deflected
directly back. This meant that Thomson’s plum pudding model was incorrect. The only
way the alpha particles would deflect directly backwards is if the mass of the atom was
concentrated in the nucleus. This is how Rutherford came up with the atomic planetary
model.
Plum Pudding Model
Atoms are made up of electrons which are negatively charged particles. Atoms
are electrically neutral, which means they have some positively charged particles as
well. Scientists in the early 20th century became curious about how many charged
particles were in the atom and how they were arranged.
Thomson was the first scientist to respond to
proposed an atomic model. In Thomson’s model each
positively charged fluid. Thomson mad the suggestion
negative charges. This model was called the plum
electrons are like raisins dispensed in pudding
these curiosities. In 1904 he
atom was a sphere filled with
that the positive fluid held the
pudding model because the