Download Ernest Rutherford

ANCIENT TIMES
"There
is
nothing
everything
else
- Democritus from Abdera
but
is
atoms
only
and
an
space,
opinion"
To
assure you the best understanding and to let you have a closer look at the
development of atomic physics' thoughts and ideas we will start our scientific journey
from the achievements of ancient Greek philosophers therefore going back in time for
over two thousand years. The man we are going to tell you now about were the first ones
to research the structure of the world. As it was so long ago no wonder that researches
they did were in considerable range (but fortunately not always) limited to solely logical
considerations which were not supported by any experiments or more discerning
observations of nature. It is not hard to guess that the fact caused lots of contradictions
and often divergence between theory and practice.
Thales from Miletus (625 - 545 B.C.) started to considerate the
structure of the world as one of the first Greek thinkers. What he is very
well known for is that he noticed and described the electrical influence
of amber electrified by rubbing (anyway it is quite a god way to check
if it's a real amber you have bought: rub it quite fast with a piece of
wool and then place it near your hair. If the stone doesn't attract your
hair - sorry but it isn't a real amber). He also recognised water as a basic
substance occurring in nature thinking it was an original and final
element. Life also descended from water which in turn was as he said a
source of all motion. For Thales water had all needed features to let the
whole nature develop. He was wrong of course but just think - after all
he discovered the importance of motion and he considered the nature of
force! Did you know that he came to the conclusion that force is united
with matter?!
Anaximander from Miletus (611 - 547 B.C.), was Thales's disciple. He perceived
world in quite a simple way - as the composition of contrasts: dry and wet, hot and cold.
You might think that quite a smart teacher had quite a silly disciple. Well... not exactly
because Anaximander said that one contrast element couldn't came from the other and it
would be a mistake to declare any one of them as a basic element. "So what" you may say
again. So what?! Think! He found out that there is more than one basic substance.
Nowadays we call them chemical elements. Think again! - There was a man living before
Christ who knew that some things cannot change into others just as we today know that
for example copper cannot be changed into gold and vice versa!
That is not all about him - he believed in the subsistence of substance he called
"apeiron". He thought it was a great, infinite in time and space, undiverted and neutral
immensity. Strange features? Well, as for us apeiron resembles something well known
nowadays - vacuum! Of course Anaximander wasn't always that right: He said that
apeiron filled the whole world and was a creative element of all the other substances
which later disappeared in it. According to Anaximander oppositions included in apeiron
could separate. What he also maintained is that matter was combined with motion making
a
unit.
And what do you think about him now?
Anaximenes from Miletus (585 - 525 B.C.), was another of Thales's disciples.
Although the names of both Thales's disciples sound very similar try not to mismatch
them because their thoughts were different. Anaximenes maintained that basic substance
was not water as his teacher said neither apeiron like his college said but air. By
Anaximenes it was to be infinite in quantity. His observation of nature confirmed that. He
said all other things could be created in the process of air thickening (while cooling it
down), and the process of air rarefying (during warming it up). For example, fire was to
be created by air rarefying but winds, clouds, water, earth and other solid substances by
air condensation. Such thermal conversions he connected with everlasting movement in
the universe. He used mentioned above considerations to explain weather conditions. Isn't
it great that he knew so much about the nature of gases?! So we hope you will never
again say that you can't tell Anaximander from Anaximenes.
Heraclitus from Ephesus (540 - 480 B.C.). The substance he
considered the basic one was fire. His conclusion was that fire could
change into all other elements and substances while coming through
the universe from its top to bottom (fire changed into air, air into
water and water into earth).
Xenophanes from Colophon (575 - 480 B.C.) completed the list of elements because
as the original substance he considered earth - the fourth element.
Parmenides from Eleusis (540 - 470 B.C..) defined "being" as everything
perceptible for the mind. Being didn't have the beginning and was unchanging. He
thought that being was not connected with time and spreaded over everything. Doesn't it
sound like a beautiful religion? Anyway he also maintained that no substance could
change into other. What's quite funny as his image of the world was not in agreement
with the observations (f. e., wood burns down, water evaporates - nothing is unchanging)
his conclusion was that one shouldn't at all believe his senses, but only his reason.
Empedocles from Acragas (490 - 430 B.C.) maintained that matter consisted of four
substances. As you probably have guessed those four were to be elements: earth, fire,
water, and air. What you will find nothing new none of them have the right to change into
another. As you see the Greek philosophers influenced each others thoughts very much.
But why we tell you about Empedocles is the new thing in the ancient considerations: He
maintained that all the things were built of the four elements but combined in different
proportions. For example, he said, bones were made of two pieces of earth, two pieces of
water and four pieces of fire. After their combination the new substance was created, but
the elements stayed unchanging. Smart, wasn't he! He was also quite romantic stipulating
the subsistence of two original forces necessary for world's existence: love and discord.
The forces were working by attracting and repelling. Love combined common particles
and hate repulsed different particles. Unfortunately we have to say one more think about
Empedocles - he was against the theory of vacuum. Well...
Anaxagoras from Clazomenae (500 - 428 B.C.) also stated that world's components
were unchanging. Just like Empedocles he was of the opinion that particles could
combine with each other and disintegrate. But his all new idea was that each and every
substance had its own kind of particle, called by him "nucleus". According to
Anaxagoras there was the infinite number of nucleuses and they could be divided
endlessly. For the first time we find here the opinion that matter consistence is more
complicated then (combination of) four elements. Anaxagoras stipulated that each and
every particle contained all the other particles in different proportions. His example was
that eating particles of meat one ate also the particles of muscles, bones and blood,
building up his organism in this way.
Leukippos (probably about the 5th century B. C.) asserted that world consisted of
indivisible particles of matter. They should have geometrical shapes and were called
"schematones". He said that they had definite place in space. They were not detected by
senses because they were not connected with them, but with reason. They sent secondary
particles which got to one's soul leaving there the reflection of the external world. The
most important thing you should remember about him is that he postulated also the
subsistence of some empty space where elementary particles could be placed. The void
was needed to let the particles move. He laid the foundations of the theory explicated
later
by
Democritus.
The problem with Leukippos is that his existence is quite doubtful. Maybe he was only
the character created by Democritus.
Democritus from Abdera (460 - 370 B.C.) the greatest, the most
important Greek philosopher engaged with the problem of world's
structure. Indeed, it is from his times that the development of atomic
physics dates. "On the Little Order of the World" is the title of his work
where he described his theory. "Nothing can change into something
absolutely different" he said. He saw nature as the ceaseless motion of
small, material, indivisible and eternal particles. So they could not be
created not annihilated and were unchanging. "Indivisible" in Greek is
"atomos", so Democritus called his particle atom. Would you like to
know what made us still use the same name today? First of all Democritus called this way
the particle he imagined to be the basic brick of matter. Then - it had a shape and place in
the space. Before Democritus people believed that matter was built of something so
abstractive that it couldn't be sees because it had no "look-like". But his point of view
was different and he even believed that atom had some mass. Seeing that things are so
much various, he came to the opinion that atoms couldn't be identical, but of different
shapes and sizes. These differences were influencing features of materials. He imagined it
this way: White things were made of smooth atoms and black of rough ones. Sweet
things were made of spherical atoms and bitter of angular ones. He also believed that life
consisted of very small, round, smooth atoms and soul was mode of the smallest particles
of air and heat. Later on Democritus ascertained that hard things were made of many
atoms without much space between them and soft things were made of loose atoms. Then
he said that particles situated in empty space could move all the time with similar atoms
approaching and different repulsing; sometimes colliding, bounding and gathering into
groups. For him the universe was an act of perpetual gathering and diffusing of atoms
kept
in
everlasting
motion.
It is hard to believe that he could came to all this using only his reason, having no
laboratory neither any experimental equipment.
Epicurus (342- 270 B.C.) maintained that there were indivisible atoms
having their own size, weight and shape. Everything in the universe was
made of them including human's body and soul. In empty space atoms
could move uniformly up and down thanks to the gravitation. But they
could also abberate at random and turn. Such description of the
movement of particle made randomness and freedom possible!
Titus Lucretius Carus (95 - 55 B.C.), who was a Roman, continued Epicurus's
philosophy. He wrote a monumental poem "On the Constitution of the Nature" ("De
Rerum Natura"). There he enclosed his considerations. He explained all occurrences on
the basis of atomic physics theories. Thanks to his work the opinions of Democritus and
Epicurus penetrated the Roman Empire and consolidated there. And here are some
interesting verses off his work turned by us, and unfortunately it is not Latin into English
translation but Polish into English one. So it is not very artistic but we hope still can give
you a view on his ideas:
" ...And we see the stone pavements of the highroads abraded
Blank by the feet of the crowd; standing in gates bronze
Statues also show, how their right hands grow thin
Touched over and over again by the many of greeting passers-by.
We see than, that it all become lose of abrasion,
But the jealous Nature won't let you
See, what particles run away there all the time.
And also even the most sharp-eyed one can't see
Trying the hardest he can, the particles which Nature every day
Secretly adds to the things, ordering them to slowly grow... "
Aristotle (384 - 322 B.C.) was especially respected in Middle Ages
with the bad event for atomic physics must say. He was a resolved
opponent of Democritus's atomic physics. He stated that world
couldn't consist of small, indivisible particles because if so they should
fell down like a thrown up rock did. Do you remember Anaximander
from Mileus? Well, Aristotle stated something very similar to that: He
was of the opinion that there were four basic qualities determining the
constitution of substance. Those four were to be: dryness, wetness,
heat and cold. For example, fire consisted of heat and dryness; water
consisted of cold and wetness. The conversion of water into steam he
explained in that way: The heat of fire joins the wetness of water
creating air and earth (the last one can be found at the bottom of the
pot after vaporising the water). Those qualities were abstract. The
vision created by him buried Democritus's theories for many centuries
and that is why we have told you about the not very interesting ideas
of Aristotle.
Greek philosophers achieved very much in the world's construction understanding.
Although their thoughts were rather philosophical than natural scientific, still great. Only
uncommon people could dare to make an attempt to understand and describe rationally
the universe. The achievements of the philosophers began the history of atomic physics'
development. The conception of atom was formulated. Philosophers tried to describe it
but without the possibility of checking the presumptions experimentally. It led to many
different, contradient theories. One can say that every philosopher had a different opinion
on microstructure. Unfortunately, in Middle Ages people chose wrong theory (Aristotle's
one). Nevertheless Democritus's works prevailed again in contemporary times
influencing scientists.
1Democritus & Aristotle
2. Lavoisier
3 Dalton
4. Thomson
5. Millikan
6 Rutherford
7 Bohr
1. Democritus of Abdera & Aristotle
http://library.thinkquest.org/19662/low/eng/ancient.html#Demokryt
http://members.tripod.com/~mrbeens/atom.html
http://www-groups.dcs.st-and.ac.uk/~history/Mathematicians/Democritus.html
http://www-history.mcs.st-andrews.ac.uk/history/PictDisplay/Democritus.html
http://www.rit.edu/~flwstv/aristotle1.html
http://www.perseus.tufts.edu/GreekScience/Students/Marc/short_paper.html
http://www.utm.edu/research/iep/d/democrit.htm
o In what period of time did they live?
o What is their country of origin?
o What were their views/models of the atom?
o Were their beliefs accepted by society at that time?
Antoine Lavoisier
Antoine-Laurent Lavoisier is best remembered as a
genius in the field of chemistry. After conducting a series
of elegant experiments, he named oxygen and overturned
the phlogiston theory of Joseph Priestly, though Lavoisier
probably could have been a little more generous in
acknowledging the groundwork laid by Priestly's efforts.
From The Lunar Men by Jenny
Uglow
Born in 1743 to a wealthy upper-middle-class family,
Lavoisier was elected to the Académie des Sciences at the
age of just 23. Soon after, he shocked many of his friends
and colleagues by joining a deeply despised profit-driven
tax-collecting firm and marrying the 13-year-old daughter
one of the firm's senior members. The marriage's
prospects might not have looked promising, but Lavoisier
and his wife Anne-Marie proved to be a devoted, if not
necessarily faithful, couple. She became his reliable lab
assistant and even learned English to keep her husband
abreast of scientific developments across the Channel.
Lavoisier was a polymath. He made advancements in minerology, ballooning, street
lighting, and even established a model farm and an organization for famine relief —
putting at least some of the money he made collecting taxes to good use. Though he
wasn't really educated in natural history, Lavoisier also made exceptional contributions to
geology.
In 1766, Lavoisier began working with the geologist Jean-Etienne Guettard to create
geological maps of France. At the time, most geologists believed that earth's ancient
landmasses had been submerged under a giant ocean, and that this universal sea was
responsible for the layers of sediments they found. Lavoisier's studies led him to reject
this notion for a more complicated (and accurate) explanation.
From The Lying Stones of Marrakech by Stephen Jay Gould
In his mapping efforts, Lavoisier recognized two distinct kinds of sediment layers. One
kind often contained thin, delicate, well-preserved shells that must have been deposited
gently. The other contained no well-preserved shells, but lots of rounded pebbles.
Lavoisier deduced that the pebbles had been smoothed by agitated water. He named the
first kind of sediment pelagic beds, and the second kind of sediment littoral beds. Further,
he hypothesized that the two kinds of beds resulted from alternately rising and falling sea
level, and that the roughened-up littoral beds were nearer coastlines.
So many advances and retreats of the sea, and such a peaceful deposition of pelagic
sediments suggested to Lavoisier "an immense span of years and centuries." He also
recognized that some sediment layers preceded any discernible fossils, but more recent
sediments contained them. He ultimately concluded that the earth was originally devoid
of life, then developed land-based vegetation, then developed animals on land and in the
sea.
Lavoisier published his insights in 1789, including the explanatory diagram shown above.
Just five years later, he was dead, sent to the guillotine in the Terror of the French
Revolution. One of his surviving friends remarked, "It took them only an instant to cut
off his head, but France may not produce another like it in a century."
We might as well attempt to introduce a new planet into the solar system, or to annihilate one
already in existence, as to create or destroy a particle of hydrogen.
John
Dalton,
A
New
System
of
Chemical
Philosophy,
1808)
John Dalton (1766-1844) developed the first useful atomic theory of Vocabulary
matter around 1803. In the course of his studies on meteorology,
Dalton concluded that evaporated water exists in air as an atom
independent gas. He wondered how water and air could occupy the chemical change
same space at the same time, when obviously solid bodies can't. If hypothesis
the water and air were composed of discrete particles, Dalton stoichiometry
reasoned, evaporation might be viewed as a mixing of water particles
with air particles. He performed a series of experiments on mixtures of gases to
determine what effect properties of the individual gases had on the properties of the
mixture as a whole. While trying to explain the results of those experiments, Dalton
developed the hypothesis that the sizes of the particles making up different gases must be
different. He later wrote [1]
"...it became an object to determine the relative sizes and weights, together with the
relative numbers of atoms entering into such combinations... Thus a train of investigation
was laid for determining the number and weight of all chemical elementary particles
which enter into any sort of combination one with another."
Dalton's exceptional gift for recognizing and interpreting patterns in experimental data lead him
from a problem in meteorology to the idea of atoms as fundamental constituents of matter. He
realized the vital theoretical connection between atomic weights and weight relations in chemical
reactions. He was the first to associate the ancient idea of atoms with stoichiometry.
Some of the details of Dalton's original atomic theory are now known to be incorrect. But
the core concepts of the theory (that chemical reactions can be explained by the union
and separation of atoms, and that these atoms have characteristic properties) are
foundations of modern physical science.
Click on any image for a big picture
and more information.
ne hundred years ago, amidst glowing glass
A simple cathode ray tube.
tubes and the hum of electricity, the British
physicist J.J. Thomson was venturing into the
interior of the atom. At the Cavendish Laboratory
at Cambridge University, Thomson was
experimenting with currents of electricity inside
empty glass tubes. He was investigating a longstanding puzzle known as "cathode rays." His
experiments prompted him to make a bold
proposal: these mysterious rays are streams of
particles much smaller than atoms, they are in fact
minuscule pieces of atoms. He called these
particles "corpuscles," and suggested that they
might make up all of the matter in atoms. It was
startling to imagine a particle residing inside the
atom--most people thought that the atom was
indivisible, the most fundamental unit of matter.
homson's speculation was not
unambiguously supported by his
experiments. It took more experimental work by
Thomson and others to sort out the confusion. The
atom is now known to contain other particles as
well. Yet Thomson's bold suggestion that cathode
rays were material constituents of atoms turned out
to be correct. The rays are made up of electrons:
very small, negatively charged particles that are
indeed fundamental parts of every atom.
Thomson in his office.
odern ideas and technologies based on
"Could anything at first sight
seem more impractical than a
body which is so small that its
mass is an insignificant
fraction of the mass of an atom
of hydrogen?"
-- J.J. Thomson.
the electron, leading to television and the
computer and much else, evolved through many
difficult steps. Thomson's careful experiments and
adventurous hypotheses were followed by crucial
experimental and theoretical work by many others
in the United Kingdom, Germany, France and
elsewhere. These physicists opened for us a new
perspective--a view from inside the atom.
ROBERT ANDREWS MILLIKAN
Robert Andrews Millikan was born on 22nd March 1868 at Morrison in the United
States. In 1895 he achieved the D.Sc. degree at the Columbia University. Afterwards he
spent one year in Europe at the universities of Berlin and Gottingen. After return to his
native country he became an assistant to Albert Michelson (at the Chicago University) - a
great physicist who proved that the speed of light does not depend on the direction of
observation.
In 1910 Millikan was nominated a full professor of the Columbia University. Shortly
afterwards - in 1911 - he determined the elementary charge. In 1915 he became a member
of the American Academy of Science. In 1916 he provided an experimental proof of the
law formulated by Albert Einstein, describing the photoelectric phenomenon.
Later - in 1921 - Millikan went to California where he became the director of the
Norman Bridge Physical Laboratory at the California Institute of Technology. In 1922 he
was appointed a United States representative at the Committee for Intellectual
Collaboration of the League of Nations.
In 1923 Robert Millikan received a Nobel prize.
He was comitted to scientific activity until as late as 1945, investigating cosmic rays
and atomic structure. At the age of 77 he withdrew from scientific activity. He died on
19th December 1953.
Ernest Rutherford
1st Baron Rutherford of Nelson and Cambridge
(1871-1937)
Ernest Rutherford, physicist, who became a Nobel laureate for his pioneering work in
nuclear physics and for his theory of the structure of the atom.
Rutherford was born on August 30, 1871, in Nelson, New Zealand, and was educated at
the University of New Zealand and the University of Cambridge. He was professor of
physics at McGill University in Montréal, Quebec, from 1898 to 1907 and at the
University of Manchester in England during the following 12 years. After 1919 he was
professor of experimental physics and director of the Cavendish Laboratory at the
University of Cambridge and also held a professorship, after 1920, at the Royal
Institution of Great Britain in London.
Rutherford was one of the first and most important researchers in nuclear physics. Soon
after the discovery of radioactivity in 1896 by the French physicist Antoine Henri
Becquerel, Rutherford identified the three main components of radiation and named them
alpha, beta, and gamma rays . He also showed that alpha particles are helium nuclei. His
study of radiation led to his formulation of a theory of atomic structure, which was the
first to describe the atom as a dense nucleus about which electrons circulate in orbits
(see Atom and Atomic Theory).
In 1919 Rutherford conducted an important experiment in nuclear physics when he
bombarded nitrogen gas with alpha particles and obtained atoms of an oxygen isotope
and protons. This transmutation of nitrogen into oxygen was the first artificially induced
nuclear reaction. It inspired the intensive research of later scientists on other nuclear
transformations and on the nature and properties of radiation. Rutherford and the British
physicist Frederick Soddy developed the explanation of radioactivity that scientists
accept today. The rutherford, a unit of radioactivity was named in his honor.
Rutherford was elected a fellow of the Royal Society in 1903 and served as president of
that institution from 1925 to 1930. He was awarded the 1908 Nobel Prize in chemistry,
was knighted in 1914, and was made a baron in 1931. He died in London on October 19,
1937, and was buried in Westminster Abbey. His writings include Radioactivity (1904);
Radiations from Radioactive Substances (1930), which he wrote with British physicists
Sir James Chadwick and Charles Drummond Ellis, and which has become a standard
text; and The Newer Alchemy (1937).
The Bohr
Model
The most important properties of atomic and molecular structure may be
exemplified using a simplified picture of an atom that is called the Bohr Model. This
model was proposed by Niels Bohr in 1915; it is not completely correct, but it has
many features that are approximately correct and it is sufficient for much of our
discussion. The correct theory of the atom is called quantum mechanics; the Bohr
Model is an approximation to quantum mechanics that has the virtue of being much
simpler. (Here is a more realistic discussion of what atomic orbitals look like in
quantum mechanics.)
A Planetary Model of the Atom
The Bohr Model is probably familar as the
"planetary model" of the atom illustrated in the
adjacent figure that, for example, is used as a symbol
for atomic energy (a bit of a misnomer, since the
energy in "atomic energy" is actually the energy of
the nucleus, rather than the entire atom). In the Bohr
Model the neutrons and protons (symbolized by red
and blue balls in the adjacent image) occupy a dense
central region called the nucleus, and the electrons
orbit the nucleus much like planets orbiting the Sun
(but the orbits are not confined to a plane as is
approximately true in the Solar System). The
The Bohr atom
adjacent image is not to scale since in the realistic
case the radius of the nucleus is about 100,000 times
smaller than the radius of the entire atom, and as far as we can tell electrons are
point particles without a physical extent.
This similarity between a planetary model and the Bohr Model of the atom
ultimately arises because the attractive gravitational force in a solar system and the
attractive Coulomb (electrical) force between the positively charged nucleus and the
negatively charged electrons in an atom are mathematically of the same form. (The
form is the same, but the intrinsic strength of the Coulomb interaction is much
larger than that of the gravitational interaction; in addition, there are positive and
negative electrical charges so the Coulomb interaction can be either attractive or
repulsive, but gravitation is always attractive in our present Universe.)
But the Orbits Are Quantized
The basic feature of quantum
Quantized energy levels in hydrogen
mechanics that is incorporated in the
Bohr Model and that is completely
different from the analogous planetary model is that the energy of the particles in
the Bohr atom is restricted to certain discrete values. One says that the energy is
quantized. This means that only certain orbits with certain radii are allowed; orbits
in between simply don't exist.
The adjacent figure shows such quantized energy levels for the hydrogen atom.
These levels are labeled by an integer n that is called a quantum number. The lowest
energy state is generally termed the ground state. The states with successively more
energy than the ground state are called the first excited state, the second excited state,
and so on. Beyond an energy called the ionization potential the single electron of the
hydrogen atom is no longer bound to the atom. Then the energy levels form a
continuum. In the case of hydrogen, this continuum starts at 13.6 eV above the
ground state ("eV" stands for "electron-Volt", a common unit of energy in atomic
physics).
Although this behavior may seem strange to our minds that are trained from birth
by watching phenomena in the macroscopic world, this is the way things behave in
the strange world of the quantum that holds sway at the atomic level.
Atomic Excitation and De-excitation
Atoms can make transitions between the orbits allowed by quantum mechanics by
absorbing or emitting exactly the energy difference between the orbits. The
following figure shows an atomic excitation cause by absorption of a photon and an
atomic de-excitation caused by emission of a photon.
Excitation by absorption of light and de-excitation by emission of light
In each case the wavelength of the emitted or absorbed light is exactly such that the
photon carries the energy difference between the two orbits. This energy may be
calculated by dividing the product of the Planck constant and the speed of light hc
by the wavelength of the light). Thus, an atom can absorb or emit only certain
discrete wavelengths (or equivalently, frequencies or energies).
Here is a Shockwave movie of atomic absorption and emission (requires the Flash 2
Shockwave Plugin, which is available for free from Macromedia for Windows and
Macintosh systems). Here is a Java applet illustrating atomic absorption and
emission