Download JJ Thomson`s Model of the Atom

ATOMIC MODELS OF THE ATOM
Who are these men?
In this lesson, we’ll
learn about the men
whose quests for
knowledge about the
fundamental nature of
the universe helped
define our views.
During the middle
ages (492 – 375 BC),
Aristotle and
Plato
postulated that
there were only 4
types of
“elements”.
Earth, Fire, Water, Air.
This was supported by Empedocles
Why?
Aristotle and Plato favored the earth,
fire, air and water approach to the
nature of matter. Their ideas held
sway because of their eminence as
philosophers. The atomos idea was
buried for approximately 2000 years.
Different combinations of these led
to “stuff”.
Democritus
• This is the Greek
philosopher Democritus
who began the search for a
description of matter more
than 2400 years ago.
– He asked: Could matter
be divided into smaller
and smaller pieces
forever, or was there a
limit to the number of
times a piece of matter
could be divided?
400 BC
In 400 B.C. A Greek Philosopher by the
name of Democritus had an interesting
variation of the 4-element hypothesis:
He claimed that there was a point at which
matter could no longer be broken down.
His theory suggested that elements are made
up of small indivisible particles called atoms.
(atomos meaning indivisible)
Atomos
 To Democritus, atoms
were small, hard
particles that were all
made of the same
material but were
different shapes and
sizes.
 Atoms were infinite in
number, always moving
and capable of joining
together.
Democritus’
Model of the
ATOM
Dalton’s Model
Many scientists were
busy studying the natural
world, experimenting and
analyzing. In 1803 –
1807, John Dalton, a
British scientist and
teacher developed the
first atomic theory
based on his own work
and the work of many
others that came before
him.
The 4 main points of Dalton’s Atomic theory are:
1.
Atoms are smallest building blocks of matter.
2.
In a chemical reaction Atoms are neither created
or destroyed,only rearranged differently
3.
Atoms of the same element are identical (i.e have
the same properties such as mass & size). Atoms
of different elements are not the same.
4.
Atoms of different elements combine to form
compounds in specific proportions.
Dalton’s Model of the Atom
Atom is solid and indivisible
much like a “BILLIARD
BALL”.
.
• This theory
became one of
the foundations
of modern
chemistry.
Thomson’s Plum Pudding Model
• In 1897, the
English scientist
J.J. Thomson
provided the first
hint that an atom is
made of even
smaller particles.
Thomson Model
• Thomson studied
the passage of an
electric current
through a gas.
• As the current
passed through the
gas, it gave off
rays of negatively
charged particles.
Thomson Model
• This surprised
Thomson, because
the atoms of the
gas were
uncharged. Where
had the negative
charges come
from?
Where did
they come
from?
J.J. Thomson dramatically changed the
modern view of the atom.
Thomson concluded that the
negative charges came from
within the atom.
A particle smaller than an
atom had to exist.
The atom was divisible
Thomson called the
negatively charged
“corpuscles,” today known as
electrons.
J.J. Thomson’s Model of the
Atom
Thomson's work suggested that the atom was a
positive sphere (most of the mass of the atom) with
negative electrons imbedded throughout. The charges
balance out so the atom was neutral. “BLUE BERRY
MUFFIN or CHOCOLATE CHIP COOKIE MODEL”.
Rutherford’s Gold Foil Experiment
• In 1908, the English
physicist Ernest
Rutherford was hard
at work on an
experiment that
seemed to have little
to do with unraveling
the mysteries of the
atomic structure.
The next atomic development came
about 10 years later in 1911. A New
Zealander by the name of Ernest
Rutherford (mathematician and
physicist) tested Thomson's hypothesis
by devising his famous "gold foil"
experiment.
Rutherford reasoned that if Thomson's model was
correct, then the mass of the atom was spread out
evenly throughout the atom and there would be very
little to deflect the high speed alpha particle (helium
nuclei). All of the alpha particles should go through!
As expected, most alpha particles went right through the
gold foil atoms but to his amazement 1/10 00 alpha particles
deflected or rebounded almost directly backwards.
Therefore, there must be a hard core in the middle!
Rutherford’s
Observations
Almost all alpha particles
went through the atom
1/ 10 000 alpha particles
deflected or reflected
Conclusions
Atom is mostly empty space
Hard core in the middle of
the atom called the
‘nucleus’(most of the mass)
Rutherford’s Model
of the Atom
An atom of mostly empty space with tiny hard core nucleus
where most of the mass of the atom was contained.
Electrons hover around the nucleus like bee’s around a hive.
Bohr Model
• In 1913, the Danish
scientist Niels Bohr
proposed an
improvement. In his
model, he placed
each electron in a
specific energy
level.
The next important development
came in 1914 when Danish physicist
Bohr had doubts about Rutherford’s model of the atom.
Bohr
revised
thearound
model
again.would
He Niels
knew that
electrons
hovering
a nucleus
eventually lose energy and collapse into the middle of
the atom. This did not occur!
It had been known for some time that the
light given out when atoms were heated
always had specific amounts of energy, but no
one had been able to explain this.
Energy
 In studying the line spectra of Hydrogen through
a spectroscope, Bohr suggested that the electrons
must be orbiting the nucleus in fixed energy levels
or shells.
 The colours produced in a line spectra is a result of
'excited' electrons falling from various higher energy
levels back to their ground states.
 The energy of an electron is “quantized”.
Bohr’s Model of
the Atom
Planetary model of the atom.
Nucleus with protons and
neutrons. Electrons orbiting
the nucleus.
Bohr Model
• Electrons orbit around the nucleus in energy levels (shells).
Atomic bright-line spectra was the clue.
(c) 2006, Mark Rosengarten
Wave Model
The Electron – wave or particle
• Electrons display properties of both.
To think of them as a particle is easy
because they have a small amount of mass.
There is evidence of wave behavior though.
• http://www.youtube.com/watch?v=4cILynogu8&feature=related
The Wave Model
• Today’s atomic
model is based on
the principles of
wave mechanics.
• According to the
theory of wave
mechanics, electrons
do not move about
an atom in a definite
path, like the planets
around the sun.
Quantum-Mechanical Model
• Electrons are found in orbitals, regions of space where an
electron is most likely to be found.
• You can’t know both where the electron is and where it is
going at the same time.
The Wave Model
• In fact, it is impossible to determine the exact
location of an electron. The probable location of an
electron is based on how much energy the electron
has.
• According to the modern atomic model, an atom has
a small positively charged nucleus surrounded by a
large region in which there are enough electrons to
make an atom neutral.
Electron Cloud:
• A space in which electrons are
likely to be found.
• Electrons whirl about the nucleus
billions of times in one second
• They are not moving around in
random patterns.
• Location of electrons depends
upon how much energy the
electron has.
http://www.youtube.c
om/watch?v=yKgSSP
kgldk&feature=related
Electron Cloud:
• Depending on their energy, electrons are locked
into a certain area in the cloud.
• Electrons with the lowest energy are found in
the energy level closest to the nucleus
• Electrons with the highest energy are found in
the outermost energy levels, farther from the
nucleus.
Indivisible Electron
Greek
X
Dalton
X
Nucleus
Thomson
X
Rutherford
X
X
Bohr
X
X
Wave
X
X
Orbit
Electron
Cloud
X
X
Quantum Mechanic Model of the Atom
Probability of finding an electron in a region of
space
Quantum numbers
Principal Quantum number- indicates the main energy levels
surrounding a nucleus, sometimes referred to as shells or orbitals.
(1,2,3,4,5,6,7) Larger numbers are farther away from the nucleus and
electrons found here have more energy.
Orbital quantum number- indicates the shape of an orbital.
Often referred to as sublevels or subshells. (s,p,d,f in order of
increasing energy)
s orbitals can hold 2 electrons
p orbitals can hold 6 electrons
d orbitals can hold 10 electrons
f orbitals can hold 14 electrons
An alternative notation for wave functions with orbital quantum number is
Magnetic quantum number- indicates the orientation of
an orbital about the nucleus. (x,y.z coordinates)
s shape orbital: 1 orientation
ml = 0
p shape orbital: 3 orientations
ml = -1, 0, +1
d shape orbital: 5 orientations
ml = -2,-1,0,+1,+2
f shaped: 7 orientations
g shaped: 9 orientation
Spin quantum number- indicates the spin of an electron
(+1/2, or -1/2)