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STANDARD MODEL
WHAT IS MATTER MADE OF?
Molecules, Atoms
Protons, Neutrons, Electrons
THE HISTORY OF THE ATOM
Democritus & Leucippus (470-400BC)
Everything is made of tiny particles, these tiny particles
can’t be broken down
Aristotle didn’t like it – Substances are made of proportion
of Earth, Air, Wind, Fire
Unwittingly inspiring a 70’s music group:
Earth, Wind and Fire https://www.youtube.com/watch?v=Gs069dndIYk
JOHN DALTON’S MODEL OF THE ATOM
(1766 – 1844)
Main Points he proposed:
 Elements are made of extremely small particles called atoms.
 Atoms of a given element are identical in size, mass, and other properties; atoms of
different elements differ in size, mass, and other properties.
 Atoms cannot be subdivided, created, or destroyed.
 Atoms of different elements combine in simple whole-number ratios to form chemical
compounds.
 In chemical reactions, atoms are combined, separated, or rearranged.
At this point the atom looked like a small sphere (no electrons, no
nucleus)
J.J. THOMSON’S MODEL OF THE ATOM
Thomson discovered the electron in 1897
Cathode Ray Tube Experiment (https://www.youtube.com/watch?v=GzMh4q-2HjM)
Known as the Plum Pudding Model
Negative electrons floating in a positively charged soup
ERNEST RUTHERFORD’S MODEL OF THE ATOM
Gold Foil Experiment 1909
Found that there was an extremely small, positively charged
nucleus in the centre of the atom
Knew that Hydrogen was lightest element - stated hydrogen nuclei
to be a new particle called a proton
ERNEST RUTHERFORD’S MODEL OF THE ATOM
Gold Foil Experiment 1909
Question: Why don’t the electrons fall directly into the
nucleus if opposite charges attract?
Answer: They must be travelling in uniform circular
motion
The electric force is the centripetal force
Didn’t work because a constant force over a distance
is constant energy that needs to be released
Whole system would lose it’s energy really quickly
ERNEST RUTHERFORD’S MODEL OF THE ATOM
Question: Why didn’t the nucleus blow apart?
Answer: There must be another force holding the nucleus
together
 Theorized that there must be another particle that can provide a force to
hold the protons together – a Nuclear force
 Called this particle the Neutron
 These were detected experimentally by a colleague in 1932
ERNEST RUTHERFORD’S MODEL OF THE ATOM
Other notable accomplishments:
 1900-1903 - Worked at McGill University, Montreal
 1917 - Split the atom - concluded that atoms were devisable
 1919 – First person to deliberately transmute one element into
another
 On splitting the atom: “We might in these processes obtain very much
more energy than the proton supplied, but on the average we could
not expect to obtain energy in this way. It was a very poor and
inefficient way of producing energy, and anyone who looked for a
source of power in the transformation of the atoms was talking
moonshine. But the subject was scientifically interesting because it
gave insight into the atoms”
NIELS BOHR’S MODEL OF THE ATOM
Knew about Planck’s conclusion that energy is
released in packages called photons
1913 - Examined Rutherford’s theory of electron
orbit
Concluded that electrons can only release energy in
certain amounts called quantas (the energy in a photon)
These energy levels (or orbits) were discrete (at certain
set intervals) and electrons can only gain energy and
move outwards when receiving a quanta of energy
(when a photon collides and is absorbed by them) which
moves them to the next energy level
NIELS BOHR’S MODEL OF THE ATOM
Other notable accomplishments
Determined the radius of an atom using Planck’s constant
as the basis of distance between energy levels
Determined that when atoms fall down energy levels, this
determines the spectrum of colours emitted by an atom
 The colour is a function of the light’s frequency (based on E=hλ) where the
distance between energy levels
RELATE THIS TO ELECTRIC FIELDS
As the electron falls
It’s electric potential shoots up to
negative infinity and it’s kinetic
energy shoots up to positive
infinity and everything settles in
at a definite radius in the electric
field
HOW DID THEY FIND PROTONS, ELECTRONS AND
NEUTRONS?
https://www.youtube.com/watch?v=kBgIMRV895w
DE BROGLIE’S MODEL OF THE ATOM
Louis Victor Pierre Raymond duc de Broglie
1924 - Concluded that if a light wave can have characteristics of a
particle then a particle may be able to have characteristics of a wave
Electrons behave like waves and the energy levels are really just
standing waves set up around the nucleus
By using an even number of wavelengths, he arrived at the same
conclusion as Niels Bohr, there are discrete energy levels
Einstein said “It may look crazy but it really is sound”
Evidence for the De Broglie model came with the double slit experiment
and verified the wave properties of an electron
HEISENBERG’S MODEL OF THE ATOM
Heisenberg’s Uncertainty Principle
 The more precisely the position is determined, the less precisely the
momentum is known in this instant, and vice versa
A changing view of the world…
 Newton’s classical physics said that a “real” world existed whether or not
we were there to observe it.
 We can calculate the future if we try hard enough knowing forces,
position, momentum
 Heisenberg said that you can never predict the future
 If you know where an electron is, you never know where it’s headed
making it impossible to predict the future
 Even if you had perfect instruments, uncertainty is in nature
HEISENBERG’S MODEL OF THE ATOM
The Electron Cloud Model
Since you can’t know the location and the
momentum of a particle, you can’t truly
know where an electron is
The cloud is based on the probability of
where the electron can be
SCHRODINGER’S MODEL OF THE ATOM
Schroginder’s math backed up Heisenberg’s uncertainty principle
What do you know? He wrote a paper: Quantization as an Eigenvalue Problem
• One of the most influential papers in the 20th century and created a revolution
in quantum mechanics and all of physics and chemistry
• Brought quantum theory from real to imaginary numbers!
1926 – The Schrodinger Equation
• In classical mechanics, Fnet = ma predicts all future behaviour
• In quantum mechanics, Schrodinger’s equation predicts all future behaviour
Published his famous equation
To apply the equation, the Hamiltonian operator (H) is set for the potential and
kinetic energy of the system of particles
SCHRODINGER’S MODEL OF THE ATOM
The quantum craziness begins…
• The equation implies that matter is not in one spot at any one time
but is actually a wave of possible spot with each spot is an
associated probability of being there
• You do not actually know position until you measure
• Seen through the double slit experiment
“The already ... mentioned psi-function.... is now the means for
predicting probability of measurement results. In it is embodied the
momentarily attained sum of theoretically based future expectation,
somewhat as laid down in a catalog.”
- Schrodinger
SCHRODINGER’S CAT
THE QUARK MODEL
1964 – Proposed by Murray Gell-Mann and George Zweig
 Initially only three flavours of quarks: up, down and strange
 A year later, another flavour was added: charm
 1968 – Stanford Linear Accelerator
 Deep inelastic scattering showed that the proton was contained small pointlike objects and was not an elementary
particle
 Identified later as up and down quarks
 1974 – Charm quark was identified (along with charm anti-quark)
 1975 – Top and Bottom quark were added for a total of 6 flavours
 1977 –Bottom quark was idenitified
 1995 – Top quark was identified
 We have so many particles that Oppenheimer once said you could give a Nobel Prize
to the physicist that did not discover a particle that year. We were drowning in subatomic particles.
SUMMARY
Matter Particles
All matter is made up of quarks and leptons
Force and Carrier Particles
All forces are transmitted through bosons
MATTER PARTICLES - QUARKS
 Quarks are very socialble
 There are six pairs or generations of particles that make up each
 First Generation
 Up and Down Quark
 Lightest and Most stable
 Second Generation
 Charm and Strange Quark
 Less stable, decay to up and down quarks
 Third Generation
 Top and Bottom quark (once called the Beauty and Truth quarks)
 Decay
 Each Quark also has a colour (RGB)
 Quarks combine to form colourless objects
 You would need a red, green and blue quark combined to produce a white or colourless object
NAME ORIGIN
Finnegans Wake:
Three quarks for Muster Mark!
Sure he has not got much of a bark
And sure any he has it's all beside the mark.
—James Joyce, Finnegans Wake
PROPERTIES OF QUARKS – ELECTRIC CHARGE
Has a charge of either 1/3 or 2/3 the elementary charge
Antiquarks have the opposite charges to their regular
counterparts but same mass
 Antiparticle of electron is the positron, proton is antiproton, neutron is antineutron
 If particle meets its antiparticle, they eliminate each other and release photons
Quark
Charge
Up, Charm and Top
+2/3
Down, Strange and Bottom
-1/3
Anti-Up, Anti-Charm, Anti- Top
-2/3
Anti-Down, Anti-Strange, Anti-Bottom
+1/3
TYPES OF PARTICLES
Hadrons
Has a net integer electric charge and no
colour
A few types of hadrons:
1) Baryons
 Made of three quarks (qqq)
 Example:
 Protons (uud)
 Neutrons (udd)
2) Mesons
 Made up of a quark and an anti-quark
 Because has a particle and anti-particle, it is very unstable
 Life lasts 100th of microsecond
MATTER PARTICLES - LEPTONS
Loners of the particle field
There are six pairs or generations of particles that
make up each
 First Generation
 Electron and Electron Neutrino
 Second Generation
 Muon and Muon Neutrino
 Third Generation
 Tau and Tau Neutrino
Charge and Mass
 Electrons, Muons and Taus have sizable mass and a charge
 Neutrinos have very little mass and no charge
FORCE AND CARRIER PARTICLES
Four fundamental forces in the universe
Weak Force
 Stronger than gravity, weaker than strong and EM, acts over a very short range
Strong Force
 Strongest of all forces, acts only over a very short range (subatomic particles)
Electromagnetic Force
 Many times stronger than gravity, infinite range
Gravitational Force
 Weakest, infinite range
Forces are created by the exchange of force carrier particles
called Bosons
THE FORCE CARRIER PARTICLES - BOSONS
• Matter exchanges energy with other particles through the exchange of
Bosons
• Bosons are the glue that hold matter together
• Forces aren’t things that just happen, it is a thing that is passed between
particles (a boson)
Force
Force Carrier (Bosons)
Weak
W and Z Boson
Strong
Gluon
Electromagnetic
Photon
Gravity
Graviton? (Hasn’t been found yet)
Mass
Higgs
WHY IS THE HIGGS BOSON SO IMPORTANT?
STANDARD MODEL WORKS WELL…
For small scales
 All the forces applied to very small particles are very well represented by
the standard model
 Gravity isn’t well represented but is negligible at a very small scale
Quantum Theory (used for small things) and General theory of relativity (used for big
things) are proving difficult to incorporate into one framework
QUESTIONS STILL TO BE ADDRESSED
How do we incorporate gravity into the standard model?
How does dark matter fit in to the standard model?
What happened to antimatter after the big bang?
Why are there three generations of quarks and leptons at such different sizes and
scale?
Explanation of the Standard Model
https://www.youtube.com/watch?v=K6iqE8AigE
STRING THEORY MODEL
• What makes up all the particles in
the standard model?
• Tiny vibrating strings
• String theory has issues:
• Requires 10 space time
dimensions
• How many do we see?
• Even the part that is understood
seems to have a math problem