Transcript Atomic Theory - St John Brebeuf

Atomic Theory (Unit 8)
Introduction
Atomic Theory
Theories in science are proposed to explain the evidence available at the time.
As new evidence is discovered, theories are adapted to explain new data.
This is the nature of Science.
In the future this will continue.
Plato
Democritus
460-370 BC
First Greek philosopher to
suggest that tiny different
pieces of particles exist
“atoms”
Atoms make up the world
His idea was refuted by
Aristotle
Plato
Teacher of Aristotle
Aristotle
384-322 BC
Four Elements
Forces
Properties
The Four Element Theory
Aristotle harmony
wetness
conflict
Water
Air
coldness
hotness
Earth
Fire
dryness
The Four Element Theory lasted for about 2 thousand years because no
one tested the theory with scientific experiments.
It was not a scientific theory- which is tested by experiment.
Science back then was more of a philosophical moralistic field that
philosophers rather than experimentation decided.
John Dalton
1766-1844
Re-visited the idea of Atoms
Atomic Theory
Dalton’s Atomic Theory- 1808
Evidence
1.
The Law of Conservation of Mass
2.
The Law of Constant Composition- water is 11 % H
and 89 % O
Theory
1.
Each atom is an indestructible and unique spherical
particle
2.
Atoms combine in simple whole number ratios to
form compounds
Hydrogen
Oxygen
Dalton Theory- Water
1gH
1gH
16 g O
18g O
Dalton Theory- Water
16 g O
1gH
1gH
18g O
Dalton Theory- Water
16 g O
1gH
2 gH
x
18 g H2O
1gH
100%
=
11% H
89 % O
Having a molecule (atoms
combine in simple whole # ratios)
explains the law of constant
composition.
Still
11 % H
89 % O
No matter how much water you have it’s still 11% H
2H2
+ O2

2H2O
If the atoms are not destroyed then the mass does not change
J. J. Thomson 1871-1937
He discovered the
“electron”
Plum Pudding
model/blueberry muffin
model
The Thomson Theory of the Atom
The atom is made up of positive material with negative
particles throughout- like blueberries in a blueberry
muffin.
We now know this is not true…electrons are not found
inside the nucleus
Ernest Rutherford 1871-1937
He was J. J Thomson’s student
The Rutherford Atom 1911
Evidence: Gold Foil Experiment
1.
99.99 % of alphas are not deflected
2.
0.01 % of alphas are radically deflected
Theory
1.
Most of the atom is empty space.
2.
There is a small dense nucleus in the center of the
atom that makes up most of the mass. Electrons
circle the nucleus randomly.
The Rutherford Atom 1911
Scale: nucleus is home plate; atom is the baseball field
Be
Nucleus- is small but has most of the mass
Nucleus- 4 protons and 5 neutrons
-
-
Electrons
Niels Bohr
• Electrons are restricted to having certain
specific energies and are restricted to
following specific paths called “orbits” at a
fixed distance from the nucleus.
• Electrons emit energy when they move from
one orbit to the other
|Niels Bohr
Electrons _________ energy/light when they move
from a high energy level to a low energy level.
Electrons __________ energy/light when they
move up from a low energy level to a high energy
level.
|Niels Bohr
Limitations of his model is that ….
It only worked for the hydrogen atom ( only atoms with
one electron)
Electrons do not really move in circular motion…the
correct description requires quantum mechanics to
answer this question…
Discovery of the Nucleus
Size of the Atom
Read pages 139-144 from your textbook. They cover the
theories we just talked about.
It is your responsibility to know what each scientist
did/contributed to the understanding of the atom.
You can do this by writing out a summary/list of each scientist’s
accomplishments.