Transcript creator of the atomic theory

Atomic Theory
Road Trip through Atomic Theory
(Yes! You should take notes on
this.)
Democritus 400 B.C.
» Atom: the smallest particle into
which an element can be divided
and still be the same substance
» Democritus: Greek
philosopher/scientist who came up
with the idea of the atom
» Atomos means “uncuttable”
» Didn’t do any experiments
John Dalton 1700’s
»
»
Dalton: British scientist,
creator of the atomic
theory
His theory states:
a) All substances are made of
atoms.
b) Atoms of the same
element are exactly alike,
atoms of different
elements are different.
c) Atoms join with other
atoms to make new
substances.
Thomson 1897
» Identified an error in Dalton’s Atomic theory
» Discovered there are small particles (called subatomic particles) within the atom. The atom was
in fact divisible (can be broken into pieces) which
wasn’t previously thought by Dalton.
» Designed Cathode-Ray Tube experiment to prove
his new theory=identified electrons.
» “Plum-Pudding Model”-atom is a positively
charged blob of material with electrons (negative
charges) scattered throughout.
Rutherford 1909
» Former student of
Thomson’s
» Created the Gold Foil
experiment: Proposed
that lightweight,
negative electrons
move in empty space
and that in the center
of the atom is a tiny,
very dense positively
charged region called
the nucleus.
Niels Bohr 1913
» Danish Scientist who
worked with Rutherford.
» Proposed that electrons
moved in paths at certain
distances around the
nucleus, called orbitals.
Higher orbitals have more
energy. When electrons
move down orbitals, light
(photons) is emitted.
James Chadwick, 18911974
» Discovered neutrons, a sub-atomic
particle with no electrical charge.
» Neutrons have the same mass as a
proton.
» Studied radioactivity and how to
split an atom by shooting protons or
neutrons at it. This led to nuclear
power and nuclear weapons.
Modern Theory: Electron
Clouds
» Erwin Schrodinger
(Austrian) and
Werner Heisenberg
(German)-explained
the nature of
electrons in the atom.
» Electrons don’t travel
in distinct paths as
Bohr predicted but
rather are likely to be
found in certain
regions called
electron clouds.
Werner Heisenberg
(1901- 1976)
» Proposed the Uncertainty
Principle: you cannot predict
the location of an electron.
Erwin Schrodinger
» Said that by observing an atom,
you are affecting what the atom
is. It could be in 2 states at once
based on the sub-atomic particles.
» Proposed “Schrodinger’s Cat”
theory.
Wave Theory
» Electrons have wave properties and
are more complicated than Bohr’s
electron orbitals.
» Electrons can behave as both
particles and waves at the same
time.
THE END! (Don’t Cry…)