Download Dalton`s Atomic Theory

Atomic Theory
The Movers and Shakers
of the Subatomic World.
Dalton
• In the early 1800’s, the
English chemist John Dalton
did a number of experiments
that eventually led to the
acceptance of the idea of
atoms.
Dalton’s Atomic Theory
• All elements are composed of
atoms. Atoms are invisible
and indestructible particles.
continued...
• Atoms of the same element
are exactly alike.
H
H
continued...
• Atoms of different elements
are different.
O
H
continued...
• Compounds are formed by the
joining of atoms of two or
more elements.
H
H
O
Questions...
• What were the four parts
of the Dalton’s atomic
theory?
• Say it again...
Was he right?
• Dalton’s atomic theory of
matter became one of the
foundations of chemistry.
• BUT it needed work…other
scientists had to modify the
theory.
Thomson
• In 1897, the work of an
English scientist J. J.
Thompson provided the first
hint that atoms were made up
of even smaller particles
• Atoms are divisible…Dalton
was wrong!
Thompson’s Model
• He stated that atoms are
made up of positively (+)
and negatively (-) charged
particles
And...
• He thought the positive (+)
and negative (-) particles were
s p r e a d o u t in atoms like
ppuldudmisn
• (plums in puddin’)
Questions...
• What kind of particles did
Thompson find in atoms?
• What did his idea of an
atom look like?
Was Thomson Right?
• Not really…there are
positively (+) and
negatively (-) charged
particles inside atoms.
•BUT...
Rutherford’s Model
• In 1908, Rutherford
discovered the nucleus.
• He stated that atoms have a
small, dense, positively (+)
charged ce
nucleus.
nter called a
Questions...
• What did Rutherford find
inside the atom?
• What did Rutherford’s
atom look like?
So...
• Particles are not spread out
like plums in pudding…
• Positive particles (protons)
are in the center (nucleus).
• Where are the negative
particles (electrons)?
Bohr’s Model
• In 1913, Niels Bohr proposed
an improvement to
Rutherford’s Model:
• Electron’s move in definite
orbits around the nucleus, like
planets around the sun.
Questions...
• What did Bohr propose?
• Where were the particles
in Bohr’s model of an atom?
• What did it look like?
• What was special about the
electrons in Bohr’s model?
Are we there yet?
• Bohr’s model was used for a
long time…
•BUT...
Modern Atomic Model
• An atom has a small, positively
charged nucleus surrounded
large region
by a
in
which there are enough
electrons (-) to make the
atom neutral (0).
E
E
E
E
E
PPP
P PP P P
PP P P
E
E
E
E
E
E
E
Questions...
• Do electrons have specific
orbits in the modern
model?
• What does the atom look
like in the new model?
Make Your Timeline
• After the sheet is passed out:
– write your name on it!
– Fill out the timeline according
to date, scientist, notes, and
picture (if there is one) for
each scientist we went over.
– Neatness counts!!!!!
– HAVE FUN