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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