Download Atomic Theory

History of the Modern Atomic
Theory
Chemistry
The Atomic Theory
• What do we know about atoms?
• We know that atoms are composed of protons, neutrons,
and electrons. The protons and neutrons comprise
almost the entire mass of the atom and make up the
nucleus. The electrons are in energy levels outside the
nucleus residing in orbitals which contain a maximum of
2 electrons. The proton gives the atom its identity, but it
is the electron which gives the atom its chemical
properties. We know that elements consist of different
isotopes, some of which are radioactive.
• But HOW do we know all this stuff?
• There have been MANY scientists studying the atom and
radioactivity and their studies have cumulated in this vast
knowledge of the atom and its properties.
Democritus of Abdera
• First to produce an elaborate
and systematic view of the
atomic theory.
• Said that all matter is
composed of tiny,
INDIVISIBLE particles called
atomos (today, called atoms)
John Dalton
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(1766 – 1844)
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A Quaker and English
schoolteacher who
discovered he was colorblind.
Devised the atomic theory of
matter:
All elements are composed of
atoms.
All of the atoms of an element
are identical and are different
from the atoms of any other
element.
Atoms are not created or
destroyed in a chemical
reaction.
Compounds always have the
same numbers and kinds of
atoms.
Published the first list of
atomic weights and symbols
which gave chemistry a
language of its own.
Joseph John Thomson
• J.J. Thomson
(1856 – 1940)
• Discovered that atoms
were made of pieces, not
“indivisible” as previously
thought.
• Used cathode ray tube
• Discovered that cathode
rays are composed of
negative particles that
called ELECTRONS.
Thomson’s Cathode Ray Tube
Robert Andrews Millikan
• Born March 22, 1868 in
Morrison, Illinois
• Determined the charge on an
electron in his oil drop
experiment
• Showed that the electron is an
extremely light particle
Millikan’s Oil-Drop Experiment
Ernest
Rutherford
(1871 – 1937)
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• Was a research student under J.J.
Thomson at Cambridge University
• Gold Foil Experiment: all of an
atom’s + charge is concentrated in a
small core in the center- he called it
the nucleus.
• First model of the atom with a
nucleus in the center and electrons
on the outside. (Planetary model of
the atom)
• The atom is so small that it would
take over 5 million atoms side-byside to go across your notebook
paper ; he postulated the nucleus to
have almost all of the mass of the
atom even though the nucleus is
1000x smaller than the atom itself.
• Also studied radioactivity
• Discovered and named alpha and
beta radiation
James Chadwick
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1891-1974
English physicist
Worked with Rutherford
Imprisoned at beginning
of WWI until Geiger’s
laboratory interceded for
his release.
• Discovered the particle in
the nucelus that has no
charge- the neutron
• Determined the mass of
the neutron= 1.0067.
Niels Henrik David Bohr
• Born in Copenhagen on Oct. 7,
1885 (died 1962)
• During the Nazi occupation of
Denmark, Bohr escaped to
Sweden where he became
associated with the Atomic
Energy Project with Albert
Einstein.
• Added to Rutherford’s model of
the atom by including energy
levels, outside of the nucleus,
where electrons are located.
• Said that electrons “jump” to
higher energy levels when they
absorb energy
Benjamin Franklin
• Franklin was well known for his
studies on electricity and as
well as his many inventions
such as the Franklin stove,
swim fins, glass harmonica,
and bifocals.
• Said there are two kinds of
charges- (+) and (-).
• Said that like charges repel
and opposite charges attract
(Law of Electrostatics)
• Said that lightning is simply
static electricity
Henri Becquerel
• 1852 – 1908
• Father of Radioactivity
• Accidentally discovered
radioactivity – he placed some
Uranium on some unexposed
film. He found an image on
the film showing the crystalline
structure of the uranium. He
concluded the uranium emitted
radiation which could
penetrate paper opaque to
light. Uranium could do this
without an external source of
energy.
Marie Curie
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Born Marya Sklodowska in Warsaw,
Poland on Nov. 7, 1867; died 1934
Dreamed of a scientific career, a
concept inconceivable for a woman at
that time. Lack of finances force her to
become a private tutor.
Self-taught, she passed a physics
degree with flying colors. Studied for
her physics doctorate attempting to
further study the effects and energy of
uranium’s rays.
Married Pierre Curie, with whom she
shared a laboratory.
She discovered polonium and radium
in 1898.
She along with her husband and Henri
Becquerel was awarded the Nobel
Prize for Physics for their work in
radioactivity. (1903)
In 1911, she was denied entrance into
the Academy of Science, yet soon
after she was honored with a Nobel
Prize for Chemistry for determining the
atomic weight of radium.
Dmitri Ivanovich Mendeleev
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(1834 – 1907)
Born in Siberia, the youngest of 14
children (actual number varies
from 11 to 17 depending on the
source)
Very poor, but his mother saved
money for him to attend the
university.
First learned about chemistry by
working in the glass factory where
his mother worked.
Gave us the modern periodic table
(his was by increasing atomic
masses, where ours today is
arranged by increasing atomic
numbers.
Left spaces for elements which
had not yet been discovered, but
was able to predict what
properties they would have by
their location in his table.
Henry Moseley
• (1887 – 1915)
• British chemist who studied
under Rutherford.
• Said that atoms contain a
unique (+) charge in their
nucleus and named it proton.
• Said that protons give an
element its identity (# of
protons = Atomic #)
• With the discovery of isotopes
he determine the atomic weight
was not the major player in the
periodic law, but it was the
atomic number. This discovery
made the few problems with
Mendeleev’s periodic table
disappear.
• The modern periodic table is
now based on the atomic
number of the elements.
Albert Einstein
• (1879 – 1955) in Germany
• Studied violin & Judaism from age 6 – 13
• Failed an exam which would have
allowed him to study as an electrical
engineer
• Renounced German citizenship in 1896,
became a Swiss citizen in 1901
remaining stateless for these number of
years.
• In 1900 graduated as a teacher of
mathematics and physics.
• In 1905 showed how mass and energy
were equivalent. (E = mc2)
• Explained the photoelectric effect using
Planck’s theory: light causes electrons to
be ejected when it hits a piece of metal.
There is a minimum frequency (energy)
of light needed to eject an electron.
• Said that light is composed of photon –
discrete packets of energy
• Received Nobel Prize in 1921 for his
work on the photoelectric effect.
Albert Einstein
• Left Germany in Dec. 1932 as
the Nazis came to power,
never to return.
• In 1940 Einstein became a US
citizen, retaining his Swiss
citizenship.
• In 1944, he made a
contribution to the war by
handwriting his 1905 paper on
special relativity and putting it
up for auction. It raised
$6,000,000. It resides today in
the Library of Congress.
• In 1952, after the death of the
first President of Israel, the
Israeli government offered him
this position, of which he
refused.
Antoine-Laurent Lavoisier
• Antoine Lavoisier
(1743 – 1794)
• Called the “Father of Modern
Chemistry” because of his
careful experiments and precise
measurements.
• French chemistry responsible
for the Law of Conservation of
Matter: “Matter, like energy, can
neither be created or destroyed,
only changed from one form to
another.”
• Major tool was the balance
• Recognized the role that oxygen
plays in burning and rusting
• He was beheaded during the
French Revolution.
Joseph Proust
• 1754-1826
• French chemist
• “steadiness” of the
composition of chemical
compounds
• Said that compounds
always contain the same
elements in the same
proportions (Law of
Definite Proportions)
Michael Faraday
• 1791-1867
• English chemist and
physicist
• Said that atoms are
related to electricity,
atoms contain
particles that have
electric charges
The Infamous Kite Experiment
Max Planck
• 1858-1947
• German physicist
• Stated the relationship
between energy and
frequency in his equation:
E= hv.
• Frequency and energy
are directly proportional
• Defined quantum:
unique, fixed amount of
energy absorbed and/or
reflected by an object
• Founder of Quantum
Theory
Colleagues
• Albert Einstein and
Niels Bohr.
Atoms in a Crystal
• Image of Silicon atoms
arranged on a face of a
crystal. This image was
made by a Scanning
Tunneling Microscope, a
device that “feel” the
cloud of electrons that
form the outer surface of
atoms, rather like a
phonograph needle feels
the grooves in a record.
• Einstein’s studies and
papers gave one of the
first convincing proofs
that atoms do exist as
real objects.
Einstein’s Letter to FDR
• Einstein wrote a letter
attempting to alert
President Roosevelt
of the severity of
proceeding with
nuclear reactions as a
war tool.
Arthur Compton
• 1892-1962
• Said that light
consists of tiny
particles called
photons
• Said that photons
could collide with
electrons like two
balls colliding with
each other
Werner Heisenberg
• 1901-1976
• German physicist and
one of the founders of
quantum mechanics
• Worked with Neils Bohr
• Discovered Heisenberg
Uncertainty Principle:
position and momentum
of a moving object cannot
be known at the same
time
• Nobel Prize in Physics in
1932
Louie de Broglie
• 1892-1987
• Said that moving
particles exhibit
wavelike behavior
Wolfgang Pauli
• (1900 – 1958)
• Studied under Niels Bohr.
• In 1924 proposed the quantum
spin number for electrons and
in 1925 gave the scientific
world his best known work, the
Pauli Exclusion Principle:
• Said that electrons can have
only one of two spins.
• Said that only two electrons
one orbital and that each
electron in an orbital must
have opposite spins.
• Received the Nobel Prize in
1945.
Group Portrait
What did I do?
• Antoine Lavoisier
What important contributions did I
make?
• Marie Curie
E = mc2
• Albert Einstein
• What do you know
about me?
What did I contribute to chemistry?
• Dmriti Mendeleev
Together we made something
Great!
What is this?
• Who used it to
discover the electron?