Transcript Atomic Theory: the beginning

Atomic Theory: the beginning
Chapter 3 Part I
Democritus
An Ancient Greek
Theorized about
the existence of
atoms.
Did not use
Scientific Method.
John Dalton
A school teacher in
England.
Worked out his
ideas at home.
Used Scientific
Method.
Dalton’s Atomic Theory
All Elements are composed of tiny
indivisible particles called atoms.
Atoms of the same element are
identical. Atoms of one element are
different from any other element.
Atoms of different elements can
physically mix or chemically combine
with one another in simple whole
number ratios.
Chemical reactions occur when atoms
are separated, joined, or rearranged as
a result of a chemical reaction.
Dalton’s Atomic Theory
Electrons
Atoms are know to
be divisible.
One part of the
atom, the electrons
are negatively
charged subatomic
particles.
These were
discovered by JJ
Thomson.
Possible video of Cathode Tubes
http://www.chem.uiuc.edu/clcwebsit
e/cathode.html
FoxTrot
Millikan and the charge of an
electron
http://www.britannica
.com/nobel/cap/omilli
k001a4.html
Robert Millikan carried
out experiments that
allowed him to
calculate the charge
and mass of an
electron. Charge is
one unit and mass is
1/1840 the mass of a
hydrogen atom.
Protons
E. Goldstein observed a
cathode-ray tube and
discovered rays
traveling in the
opposite direction.
He called these canal
rays and That they had
a positive charge.
We now call them
protons. Their mass is
1840 times and
electron
Neutrons
James Chadwick
confirms the
existence of the
neutron. These
have no charge but
add weight to the
atom.
How did the modern atomic model
develop?
http://www.mhhe.com/physsci/chem
istry/essentialchemistry/flash/ruther
14.swf
Development of Atomic model
It all started with
Plum Pudding.
Not this Plum
Pudding!!
This is JJ Thompson’s Plum
Pudding Model
Rutherford’s Model
Rutherford realized
from his
experiments that
the positively
charged particles
had converged into
a small “nucleus”
in the center of the
atom and were
surrounded by the
very small
electrons.
Bohr’s model
Bohr took
Rutherford’s
model one step
further and
theorized the
electrons orbit
the nucleus.
Common View: But is it correct?