Image |
Name |
Description |
|
Democritus
470-380 B.C. |
Known
as the "Laughing Philosopher" because of his joyous spirit.
First to suggest the idea of atoms (atomos - Greek "a"
meaning "not" & tomos meaning "cut").
He thought matter was composed of tiny indivisible particles - atomos.
|
|
Aristotle
384-322 B.C. |
Spoke
out against Democritus and atomism. Aristotle felt matter was
continuous.
The
Catholic Church accepted Aristotle's position and came to equate
atomistic ideas with Godlessness.
In
1624, the Parliment of Paris had issued a decree that anyone holding
or teaching a position opposed to Aristotle (including atomism)
was liable to be put to death (needless to say, atomism didn't
have a chance).
|
|
John
Dalton
1766-1844 |
English
school teacher (started teaching when he was only 12 years old)
who became known as Father of the Atomic Theory.
Devised
Dalton's Atomic Theory
- All
matter is composed of indivisible particles called atoms.
- Atoms
of the same element have the same physical & chemical properties.
- Atoms of different elements have different physical & chemical
properties.
- Two or more atoms of different elements can chemically combine
in simple whole number ratios to form compounds.
- Atoms cannot be subdivided, created or destroyed when involved
in a chemical reaction.
|
|
J.
J. Thomson
1856-1940 |
English
physicist.
Discovered
the electron in 1897 after observing that the beam of light in a
cathode ray tube is attracted to a positive charge and repelled by a negative
charge.
His
model of the atom is called the Plum Pudding Model.
In
Thomson's model electrons have a negative charge but the overall
charge of the atom is neutral. |
|
Max
Planck
1858-1947 |
Planck
was able to deduce the relationship between the energy and the frequency
of radiation.
In 1900, he announced that the energy(E) emitted by a resonator
could only take on discrete values or quanta.
E=hv (E- energy, v - the frequency of the radiation, h- constant
called Planck's constant, (6.6262 x 10-34
J s)
|
|
Albert
Einstein
1879-1955 |
In
1905 used Planck's constant and proposed that light could be described
as quanta of energy that behave as particles.
Einstein used
his particle theory of light to explain the photoelectric effect
(the release of electrons from metal when light shines on it).
This was the first use of the Planck's theory by someone other
than Planck.
|
|
Ernest
Rutherford
1871-1937 |
Student
of J.J. Thomson.
Conducted
the gold foil experiment in 1909 when he shot alpha particles
at a sheet of gold foil only 1/3000 of an inch thick.
Rutherford
expected the positively charged alpha particles to pass right
through the gold foil, and most did. However, a small number of
particles were deflected off at an angle and some even bounced
straight back.
Rutherford
discoved that that the atom is mostly empty space and there is a small positively
charged core where the bulk of its mass is located. Rutherford named this small
positively charged core, nucleus (Latin, "little nut"). |
|
Robert
Millikan
1868-1953 |
Determined
the charge of the electron with his oil drop experiment in 1913.
|
|
Niels
Bohr
1891-1973 |
Student
of Ernest Rutherford
In
1913 Bohr proposed a revised atomic model. He used Planck's work
to correct a flaw in Rutherford's model.
He
placed electrons into paths of definite energy circling the nucleus.
Modeled
his atomic structure after the solar system.
|
|
Louis
de Broglie
1892-1987 |
In 1924 de Broglie discovered the wave nature
of electrons.
De Broglie
solved the electrodynamic problems with Bohr's model of the atom
in his 3 page Phd. submission that set out a relationship between
mass velocity and wavelength.
During
World War I de Broglie served in the army. He was attached to the
wireless telegraphy section for the whole of the war and served
in the station at the Eiffel Tower. |
|
Erwin
Schrödinger
1887-1961 |
Schrödinger wrote and solved a mathematical equation describing
the location and energy of an electron in a hydrogen atom in 1926.
Schrödinger's
equation is the current description of the electron in the atom.
This mathematical model is called the quantum mechanics model.
|
|
Werner
Heisenberg
1901-1976 |
In
1927 Heisenberg developed his uncertainty principle which explains
that it is physically impossible to measure both the exact position
and the exact momentum of a particle at the same time. The more
precisely one of the quantities is measured, the less precisely
the other is known.
Heisenberg's
principle proved that Bohr's model of the atom is incorrect. |
|
James
Chadwick
1891-1974 |
Student of Ernest Rutherford.
In 1932 Chadwick proved the existence of neutrons.
|
