Download 2 - History of the Atom

History of the Atom
Democritus
·
Suggested matter was made of
very small particles that could not
be broken down further.
·
He called the particles atoms, after the Greek word
atomos, which means "uncuttable".
Aristotle
·
Believed that matter was
composed of four "elements":
(earth, air, fire and water) despite the more recent "atomic"
model.
John Dalton
·In 1808, Dalton proposed the first "modern" atomic theory:
o
the atom is the smallest particle of matter.
o
atoms cannot be created or destroyed
o
each element has its own kind of atom.
o
compounds are created when atoms of different elements combine.
·He proposed the atom was a solid
sphere that looked like a billiard ball.
Jons Berzelius
·
In 1811, he introduced the classical system of chemical
symbols
·
In 1826, he published a table of atomic weights
Dmitri Mendeleev
·
In the 1860’s, he created the
first periodic table
J.J. Thomson
·He was the first person to discover electrons.
·He presented the "plum pudding"
model of the atom.
·In his model, most of the atom was one large positive charge (pudding) with
several small negative charges (plums) embedded in it.
Marie Curie
·
The first woman to win a Nobel
Prize and the first to win twice.
·
Discovered the radioactive elements
polonium and radium.
Ernest Rutherford
·Well known for conducting the "gold foil experiment".
·In 1911, he presented the "nuclear model"
of the atom: the first model to suggest a nucleus with
positively charged protons and all the mass of the atom.
Negatively charged electrons are distributed in the space
surrounding the nucleus.
Neils Bohr
·Developed a theory that electrons
have different amounts of energy and
travel in stable orbits around the
atom's nucleus.
· In 1913, he presented the "Bohr model"
or "planetary model" of the atom
which is similar to a model of the
solar system.
Max Planck
·
Won the Nobel Prize for
developing quantum theory
(a subset of physics explaining the
physical behaviours at the
molecular, atomic and
sub-atomic levels).
Albert Einstein
·
Developed the general theory
of relativity
·
Won the Nobel Prize for his
discovery of the photoelectric
effect.
Robert Millikan
·
Won the Nobel Prize
for his measurement
of the charge of an electron
Erwin Schrodinger
·
In 1926, he developed a
mathematical equation that
describes the behaviour of the
electron as a wave.
·
A solution to his equation
indicates the highest probability
of finding if an
electron is in an energy level.
Louis de Broglie
·
Proposed the idea that
moving electrons could be
considered as waves,
similar to X-rays or visible light.
·
He developed a formula for
calculating the wavelength
associated with particles in
motion such as electrons.
Schrodinger AND de Broglie
·By 1930, these two proposed
the "atomic" model of the atom.
·Just like the Bohr model, electrons
have distinct energy levels.
However the exact locations
of electrons are not defined,
but the cloud location in a
region of space around the nucleus
can be predicted.
Werner Heisenberg
·
He developed the
"Heisenberg Uncertainty Principle"
which stated that it is impossible
to determine both the position
AND the speed of an electron
at the same time.
James Chadwick
·
In 1932, he discovered the neutron which was a particle in the nucleus of an
atom.