Download Atomic Models - Cloudfront.net

Atomic Models:
From Hypothesis to
Theory
http://www.youtube.com/watch?v=bw5TE5o7JtE&feature=BFa&list=PLE2B5C43C0BC88688&lf=results_main
The Greek Model
440 BC: Leucippus &
Democritus hypothesize
that matter is made of
atoms
 Explained why different
substances have different
properties
 Performed no
experiments
 Very little evidence to
support hypothesis

Democritus of
Abdera
The Greek Model

Five major points
1.
All matter is composed of atoms


2.
3.
4.
5.
too small to be seen
CANNOT be split into smaller parts
There is a void, which is empty space between
atoms
Atoms are completely solid
Atoms are homogeneous, with no internal structure
Atoms are different in size, shape, and weight
The Dalton Model



1803: John Dalton (England)
re-introduced the atomic idea
to modern chemistry
Dalton and other chemists
did experiments involving
gases and how they combine
They noticed that elements
always seemed to combine
in the same ratios (such as
1:1, 1:2, 2:3 etc)
Dalton’s Atom, 1807

To explain these observations, Dalton
hypothesized that:
 Chemical elements are made of atoms
 The atoms of the same element have the same
mass
 Atoms of different elements have different
masses (but the same general shape)
 Atoms are involved in chemical reactions but are
not changed by them

Characteristics of Dalton’s atom



uniformly dense
indivisible
solid spheres
The Thomson Model
1897: J.J. Thomson hypothesized that
there are areas of negative charge
(electrons) within the atom
 Based on experimental observations
 Called the Plum Pudding Model

Discovery of the Electron
http://www.youtube.com/watch?v=IdTxGJjA4Jw
Rutherford’s Gold Foil Experiment




Rutherford shot alpha particles at gold foil
expected the alpha particles to go through the gold
foil but be deflected- most particles did
Some alpha particles weren’t deflected, they
bounced back!
He said “It was almost as incredible as if you fired a
15-inch shell at a piece of tissue paper and it came
back and hit you."
The Rutherford Model, 1911


Atomic theory was revised to explain
Rutherford’s observations
Rutherford’s Model stated:



The atom contains a tiny dense center called the
nucleus
the volume of the nucleus is about 1/10 trillionth the
volume of the atom
The nucleus is essentially the entire mass of the
atom (the rest is mostly empty space)
The Rutherford Model, 1911

Rutherford’s Model stated:
The nucleus is positively charged
 The amount of positive charge of the nucleus
balances the negative charge of the electrons
 The electrons move around in
ethe empty space of the atom
surrounding the nucleus
3p+

e-
e-
Discovery of the Nucleus
http://www.youtube.com/watch?v=wzALbzTdnc8
The Bohr Model

Niels Bohr
applies quantum theory to
Rutherford's atomic structure
 led to the idea of electrons
moving around the nucleus in
orbits or energy levels
 emission of light occurs when
an electron moves into a
lower energy orbit.

Bohr’s Research



Electron orbit around the nucleus in seven different
energy levels, or shells.
Electrons would only occupy the lowest possible
energy level.
Electrons would only move up a level (increasing
energy) if the lower levels were full.
Atomic Scale
Modern Atomic Theory
An updated version of Bohr’s model
 Electrons move in 3-D clouds rather than
orbits
 There are three
types of particles
in the atom rather
than two

Subatomic Particles
Particle
Charge
Mass (kg)
Relative
Mass
Location
Subatomic Particles
Particle
Proton
Neutron
Electron
Charge
Mass (kg)
Relative
Mass
Location
Subatomic Particles
Particle
Charge
Proton
1
Neutron
Electron
Mass (kg)
Relative
Mass
Location
Subatomic Particles
Particle
Charge
Proton
1
Neutron
0
Electron
Mass (kg)
Relative
Mass
Location
Subatomic Particles
Particle
Charge
Proton
1
Neutron
0
Electron
-1
Mass (kg)
Relative
Mass
Location
Subatomic Particles
Particle
Charge
Mass (kg)
Relative
Mass
Proton
1
1.67x10-27
1
Neutron
0
1.67x10-27
Electron
-1
9.11x10-31
Location
Subatomic Particles
Particle
Charge
Mass (kg)
Relative
Mass
Proton
1
1.67x10-27
1
Neutron
0
1.67x10-27
1
Electron
-1
9.11x10-31
Location
Subatomic Particles
Particle
Charge
Mass (kg)
Relative
Mass
Proton
1
1.67x10-27
1
Neutron
0
1.67x10-27
1
Electron
-1
9.11x10-31
0
Location
Subatomic Particles
Particle
Charge
Mass (kg)
Relative
Mass
Location
Proton
1
1.67x10-27
1
Nucleus
Neutron
0
1.67x10-27
1
Electron
-1
9.11x10-31
0
Subatomic Particles
Particle
Charge
Mass (kg)
Relative
Mass
Location
Proton
1
1.67x10-27
1
Nucleus
Neutron
0
1.67x10-27
1
Nucleus
Electron
-1
9.11x10-31
0
Subatomic Particles
Particle
Charge
Mass (kg)
Relative
Mass
Location
Proton
1
1.67x10-27
1
Nucleus
Neutron
0
1.67x10-27
1
Nucleus
Electron
-1
9.11x10-31
0
outside
nucleus
http://abyss.uoregon.edu/~js/21st_century
_science/lectures/lec05.html
 http://dl.clackamas.edu/ch10404/dalton%27s.htm
 http://abyss.uoregon.edu/~js/21st_century
_science/lectures/lec11.html
 http://galileo.phys.virginia.edu/classes/252
/Rutherford_Scattering/Rutherford_Scatter
ing.html
