Transcript Classical data

The Atom
Mrs. DeMedio
Chemistry Chapter 4
Objectives



You will be able to:
Evaluate the factors that
influence the deflection
of a charged particle.
Compare and contrast
the atomic models of
Dalton and Thomson.
Identify the characteristics of
alpha, beta, and gamma radiation.
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Analyze how Rutherford’s atomic
model explains the results of his
gold foil experiment.
Part I-
The
Atom
Democritus
Fifth century B.C. Greek
philosopher proposed that all
matter was composed of indivisible
particles called atoms (Greek for
indivisible).
Everyone
thought
he was
CRAZY!!!!
Democritus
is
CRAZY!!!!
Nothing happened
with atoms until…
John Dalton
A. Experiment
1. Dalton experimented with
gases.
2. He studied how water could
be absorbed into the
atmosphere.
3. He also wondered why the
atmosphere was a mixture of
gases rather than a layer of
gases.
B. Results
Gases in the atmosphere were
mixed together and not layered.
1.
2.Water vapor is absorbed into
the atmosphere.
C. Inferences from experiments.
1. Dalton’s Atomic Theory
All matter is composed of atoms
and atoms cannot be made or
destroyed.
All atoms of the same element are
identical
Atoms of different elements are
chemically different.
Chemica reactions occur when
atoms are rearranged.
Compounds are formed from
atoms of the constituent
elements.
D. Dalton’s Atomic Model
1. Dalton viewed the atom as a
hollow sphere.
Dalton’s Atomic Model
Part II:
The
Electron
Thomson
A.Experiment
1. J. J. Thomson developed
an experiment to investigate
the properties of electrons.

2. Thomson designed tubes
containing electrodes. He removed
(evacuated) all the air from the
tubes. (known as "Crookes tubes"
or"Cathode Ray Tubes". )
CATHODE RAY TUBE
3. High voltage electric
current was passed between
these electrodes.
4. Ray-like emissions
proceeded from the cathode
electrode to the anode
electrode.
J.J Thomson
5.
He then brought an electrical
field comprising of a positive and
a negative plate near the vicinity
of the rays.
6. The path of rays deflected
from the positive plate to the
negative plate which showed that
these rays possessed a negative
charge.
B. Results
1. Joseph John Thomson (1897)
a. Cathode ray tube produces
a ray with a constant charge to
mass ratio
b. All cathode rays are
composed of identical negatively
charged particles (electrons)
C- Inferences from the
properties of electrons
1. Atoms are neutral, so there
must be positive charges to
balance the negatives
2. Electrons have little mass, so
atoms must contain other
particles that account for most
of the mass.
D.Atomic Model
1. Thomson’s Plum Pudding Model
a. His results led him to see
the atom as a negatively
charged base with + particles
interspersed- much like plum
pudding.
Part III:
electron
neutron
proton
The Nucleus
Rutherford
A. Experiment
1. Ernest Rutherford (1911)
a. Alpha particles (helium nuclei)
fired at a thin sheet of gold
Rutherford’s Experiment
B- Results
Very few particles were greatly
deflected back from the gold
What does that
sheet
mean about the
1.
atom?
D-Rutherford’s Atomic Model
1. The atom has a dense center,
called the nucleus, which is
positively charged.
2. The nucleus is surrounded by
mostly empty space with small
electrons floating around in the
space.
C- Inferences
Assumed that the positively
charged particles were bounced
back if they approached a
positively charged atomic nucleus
head-on (Like charges repel one
another)
1.
2. The atom had a nucleus.
a. nucleus is very small, dense
and positively charged
b. most of the atom is empty
space