Transcript File

History of the Atomic
Theory and Atomic
Structure
Democritus
(460-370 B.C.)
• Greek
philosopher
• Matter is made
of small
particles
• He named these
“ultimate“
particles atoms
Aristotle
(384-322 B. C.)
• Disputed Democritus
theory
• Always have a
smaller piece of
matter, no matter the
size
• Only 4 elements
• Theory accepted for
2000 years
• Tutor of Alexander
Antoine Lavoisier
(1743-1794)
• Law of Conservation of
Mass =
• When a chemical
reaction takes place,
matter is not created or
destroyed, just changed.
• Named oxygen
• Beheaded by guillotine
Conservation of Matter
• Matter cannot be created or
destroyed, just changed.
• In a reaction the mass you start
with is the mass you end with.
Joseph Proust
(1754-1826)
• Law of Definite
Proportions =
compounds
always have the
same proportions
of elements by
mass.
• Super radical for
his time
John Dalton
(1766-1844)
• English
schoolteacher
and Chemist
• Proved that
atoms exist
• Model a solid
sphere
• Colorblind
(Daltonism)
Dalton also….
• proposed the Law of Multiple
Proportions which led directly to
the proposal of the Atomic
Theory
• developed the concept of the
mole
• proposed a system of symbols to
represent atoms of different
elements.
Dalton’s Atomic Theory
• He developed the first atomic theory
• All matter is made up of atoms
• Atoms are indestructible and cannot
be divided into smaller particles
• Atoms of the same element are
exactly alike and atoms of different
elements are different
• In a given compound, the relative
number of atoms are constant
J.J. Thomson
(1856-1940)
• English Nobel Prize
winner
• Said atom could be
divided into smaller
parts
• Discovered
electrons
• “Plum pudding”
model of atom
• Discovered
isotopes of
elements
Thomson’s Plum
Pudding Model
• In this model, the
volume of the atom is
composed primarily of
the more massive (thus
larger) positive portion
(the plum pudding). The
smaller electrons
(actually, raisins in the
plum pudding ) are
dispersed throughout
the positive mass to
maintain charge
neutrality.
J.J Thomson & the
Electron
• Cathode-Ray Tube Experiment
–Through this experiment Thomson was able to
discover an electrons mass to charge ratio
thereby discovering the electron.
Eugene Goldstein
(1850-1930)
• 1900
• Discovered proton
(sometimes gets credit)
• Determined protons
have a (+) charge
• Anode ray experiment
• Still supported Thompson’s Plum
Pudding model of the atom
Robert Millikan
(1868-1953)
• determined the unit
charge of the electron
with his oil drop
experiment
• This allowed for the
calculation of the
mass of the electron
and the positively
charged atoms.
Ernest Rutherford
(1871-1937)
• Worked for
Thomson
• British physicist
• Discovered atom
had nucleus
• Gold foil
experiment
Rutherford’s Gold Foil
Experiment
• Bombarded thin sheet Au foil w/
positively charged alpha particles. If
plum pudding model is right, alpha
particles should sail straight through.
Some bounced back. He concluded
that atom has small, dense, positive
core called nucleus. Electrons inside
nucleus with lots of empty space
between them.
James Chadwick
(1892-1974)
• Nucleus also
contains
particles with no
charge called
neutrons
• discovery of the
neutron led directly
to the discovery of
fission and
ultimately to the
atomic bomb.
Niels Bohr
(1885-1962)
• Danish Nobel
Prize winner
• Electrons move
around nucleus
in fixed orbits
like planets do
around the sun
Francis Aston
(1877-1945)
• first person to
observe isotopes
• His work led
Rutherford to
predict the
existence of the
neutron
Louis deBroglie
(1892-1960)
• He was a prince
• Won Nobel prize in physics 1929
• Wave-particle dualitly theory of light
based upon Planck and Einstein
• This created new field of
physics – wave mechanics
Werner Heisenberg
(1901-1976)
• 1932 Nobel prize
Physics for “creation of
Quantum mechanics”
• Uncertainty principle
• “cloud” model (quantum
mechanic model)
Max Planck
(1858-1947)
• Founder of quantum theory
• Nobel prize 1918
• Revolutionized
understanding of atomic
and subatomic processes
• Planck’s constant
• Einstein used his work to
study photons
Erwin Schrodinger
(1887-1961)
• Nobel Prize 1933
• One of founders of quantum
mechanics
• Schrodinger's equation
• Schrodinger’s cat
The Atom
The
smallest particle of an element
that retains the same characteristics
of that element.
Modern Atomic Model
• Electron cloud model
• Atom has small positively
charged nucleus surrounded by
a large negatively charged
region of electrons