Download Chapter 6

Development of the
Atomic Theory
Chapter 6 Section 1
The Beginning of Atomic
Theory
• An atom is the
smallest particle
an element can
be divided into
and still have the
properties of
that element.
Ancient Greece
• Around 440 B.C., Democritus proposed
that matter is made up of “uncuttable”
particles which are always moving.
• He called the particle an atom.
Dalton’s Atomic
Theory
• All substances are made of atoms.
Atoms are small particles that
cannot be created, divided, or
destroyed.
• Atoms of the same elements are
exactly alike, but different from
other elements.
• Atoms join with other atoms to
make new substances.
Thomson’s Discovery
of Electrons
• He discovered there are small
particles inside the atom and that
atoms can be divided.
• He discovered that some particles
had a negative charge called
electrons.
• He didn’t know how they were
arranged, but thought they might
look like chocolate-chip ice cream.
Cathode Ray Tube
Rutherford’s Atomic
“Shooting Gallery”
• He aimed a beam of
positively charged
particles into gold
foil.
• Most passed
through, but some
bounced back.
The Nucleus & the Electrons
• Rutherford discovered that
atoms are mostly empty space.
• He said atoms have a tightly
packed center called a nucleus.
• He developed a new model of
the atom.
• He studied the
way atoms
react to light.
• He suggested
that electrons
travel around
the nucleus in
definite paths.
Bohr’s
Electron
Levels
The Modern Atomic Theory
• Schrodinger and Heisenberg showed that
electrons do not travel in definite paths.
• The exact path can not be predicted.
ENERGY LEVELS
• Each electron cloud
exists at a certain
energy level.
• The energy of each
electron keeps it in
motion around the
nucleus of the atom.
SILVER
The Size of an Atom
• Atoms are very small, yet
the atom was discovered
without seeing a single
atom.
• There are 20 thousand
billion, billion atoms in a
penny.
OBSERVING ATOMS
• Atoms are so small
that light waves are
too large to be used
to observe them.
• The tools that
scientist now use to
observe atoms
include the electron
microscope.
End of Section 1
Electron
Microscope
image of
Silicon Nitrate
Video