Download Development of Atomic Theory

Development of Atomic
Theory (11.1)
FAMOUS SCIENTISTS AND THEIR
THEORIES…
Democritus
 440 BCE – thought that if you kept cutting an object
in half, the piece would eventually get too small to
cut. This particle is called an “atom”.
 Thought that atoms were small hard particles made
of a single material formed into different shapes and
sizes.
Aristotle
 Thought you would NEVER end up with a particle
that couldn’t be cut…
He was
WRONG!!!
John Dalton
 Atomic Theory was published in 1803
All substances are made of atoms. Atoms cannot be
divided.
 Atoms of the same element are exactly the same.
 Atoms join with other atoms to make different
substances.

Not all of his theory
was correct!...
J. J. Thomson
 Discovered that there are smaller particles WITHIN
an atom. Disproved Dalton’s theory that atoms
could be divided into smaller particles.

Used a cathode-ray tube and discovered that ELECTRONS
were spread throughout the atom, like plums in plum pudding
(or chocolate chips in ice cream.
 Created the plum-pudding model.
Plum- Pudding model: Electrons were
located throughout an atom like
chocolate chips in ice cream.
Ernest Rutherford
 1909- Created an experiment where some atom
particles were deflected instead of passing through
gold foil. This led to the discovery that atoms are
mostly empty space with a very dense nucleus.
 When he calculated the diameter, the nucleus was
100,000 times smaller than the diameter of the
atom.
Niels Bohr
 1913 – studied how atoms react to light.
 Proposed that electrons move around the nucleus in
energy levels. Electrons were able to “jump” to
different levels.
+
N N
N
+
+
-
-
Schrodinger and Heisenberg
 Explained that electrons do not travel in definite
paths and their paths cannot be predicted.
 Proposed that there are regions where electrons are
likely to be found called the “electron cloud”.
Erwin Schrodinger Werner Heisenberg