Every atom has a nucleus which contains protons and neutrons (both these particles are known nucleons). Orbiting the nucleus, are electrons.

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Timothy Trevor Chapman
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1 Atomic Structure Every atom has a nucleus which contains protons and neutrons (both these particles are known nucleons). Orbiting the nucleus, are electrons. Proton Number (Atomic Number): Amount of protons in the nucleus In neutral atom, equals # of electrons, so can tell you about chemical properties and such Nucleon Number (Mass Number): Amount of protons and neutrons (amount of nucleons) Isotopes Atoms with the same number of protons, but different numbers of neutrons. So same proton number, different nucleon number. e.g. Hydrogen has 3 natural isotopes. You can find Hydrogen with 1 proton and 0 neutrons (Hydrogen), or 1 proton and 1 neutron (Deuterium), or with 1 proton and 2 neutrons (Tritium). Chemical properties aren t changed if you change around the amount of neutrons. Remember, that s to do with proton number. However, the stability of the nucleus is changed once you start crapping about with the amount of neutrons. Unstable nuclei is dodgy territory, as they can be radioactive and decay over time into different nuclei that is more stable. Radioactive isotopes are kinda useful tho, it s how we re able to date things. You see, all living matter contains the same proportion of the radioactive Carbon-14 (the normal one is Carbon-12), taken in from the atmosphere. Now when you cease to exist, the amount of Carbon-14 inside of you decreases over time, as it is decaying. Using the isotopic data to find the percentage of radioactive Carbon-14 that s left inside of you, scientists can calculate the approximate age of your dead corpse.

Specific Charge The ratio of a particle s charge to its mass (measured in C kg -1 ). So, essentially, as you may be able to guess, to calculate specific charge, you just divide the charge by the mass.

2 Specific Charge The ratio of a particle s charge to its mass (measured in C kg -1 ). So, essentially, as you may be able to guess, to calculate specific charge, you just divide the charge by the mass. Amazing. Unstable Nuclei The Strong Nuclear Force As we know, the electromagnetic force exists in the nucleus, but if this was the only force, the nucleons would just start flying apart. So we know there must be a force that exists in the nucleus that is stronger. This is, the strong nuclear force. Experiments have shown that the force in fact has a very short range of approximately 0.5-3fm. It s also been shown that the force works equally between all nucleons, meaning the size of the force is the same, whether it s proton-proton, neutronneutron, or proton-neutron. Alpha Emission Only happens in massive nuclei e.g. uranium and radium. The nuclei of these atoms are just too huge for the strong force to keep them stable. When an alpha particle (a helium nuclei) is emitted, the proton number decreases by 2, and the nucleon number decreases by 4. Alpha particles have a ridiculously short range.

When a nucleus ejects a beta particle, one of the neutrons in the nucleus is changed into a proton. The proton number as a result increases by one, and the nucleon number stays the same.

3 Beta-minus Emission Happens in isotopes that are too neutron rich. It is the emission of an electron from the nucleus along with an electron antineutrino, which is released in order to conserve energy and momentum. When a nucleus ejects a beta particle, one of the neutrons in the nucleus is changed into a proton. The proton number as a result increases by one, and the nucleon number stays the same. The range of a beta particle is incredibly larger than that of alpha particles. The Neutrino Scientists originally thought that beta decay only emitted an electron. They were wrong. Observations showed that the energy of particles after the beta decay was less than it was before, which did not fit with the principle of conservation of energy. A lad named Wolfgang Pauli in 1930 hypothesized that there was in fact another particle being emitted, which was carrying away some of the missing energy and momentum, and that this particle was neutral (in order to satisfy conservation of charge laws). Other discoveries then led to Pauli s theory becoming accepted, and the particle was classed as a neutrino, and was eventually observed 25 years later. Antiparticles Photons Packets of electromagnetic radiation. Electromagnetic radiation exists as photons of energy. The energy of a photon depends on the frequency of the radiation.

Antiparticles Every particle has a matching antiparticle with the same mass and rest energy, but opposite charge. Pair Production So you can actually create matter and antimatter from energy.

It also tends to happen near a nucleus, which helps conserve momentum. The usual combo, is an electron-positron pair, because they have a relatively low mass.

4 Antiparticles Every particle has a matching antiparticle with the same mass and rest energy, but opposite charge. Pair Production So you can actually create matter and antimatter from energy. Isn t Physics amazing. Pair production only happens if a photon has enough energy to produce that much mass, and only gamma ray photons have that kind of energy. It also tends to happen near a nucleus, which helps conserve momentum. The usual combo, is an electron-positron pair, because they have a relatively low mass. The minimum energy for a photon to perform pair production is the total rest energy of the end particles produced. Each particle have a rest energy of E0 so: Annihilation In essence, the complete opposite of pair production. When a particle meets its corresponding antiparticle, annihilation is the result, and the combined mass of the particles gets converted into energy. The key thing to remember here is that two photons are created as a result.

5 Classification Particle Hadrons Leptons Baryons Mesons Hadrons Particles that feel the strong nuclear force. Baryons Their defining trait is that they are made up of 3 quarks.

6 Protons and neutrons are the only 2 baryons we need to know about, and the proton is actually the only stable baryon. All baryons try to decay into a proton. So what about antiprotons and antineutrons? Well they re antibaryons. Yeah. All baryons have a baryon number of 1. Non baryons have a baryon number of 0. Antibaryons have a baryon number of -1. Baryon number needs to be conserved in all interactions. Simple. Mesons Their defining trait is that they are made up of 2 quarks (usually a quark and antiquark). Pions (π-mesons) are the lightest, with 3 different variations. π +, π -, and π 0. Yes, all with different charges. Kaons (K-mesons) are heavier and more unstable. Same thing here, K + K -, and K 0. They have a very short lifetime and decay into pions. Leptons Leptons are fundamental particles (cannot be categorized any further), but most importantly, they do not feel the strong nuclear force. The electron is an example of a lepton, and is stable, but there are also muons (u - ), which are basically like a heavy electron. They are unstable and eventually decay into ordinary electrons. The electron and muons have their own neutrino as well. Like with baryon number, leptons have a lepton number, and surprisingly enough, it s the same principle. They have a lepton number of 1, non leptons have a lepton number of 0, and antileptons have a lepton number of -1. However, there is a separate lepton number for electrons and a separate lepton number for muons, which need to be conserved separately. Interactions Forces are caused by particle exchange. When 2 particles interact, something happens to let a particle know that the other one is there. Repulsion and attraction can be explained by the bowling ball and boomerang examples.

These exchange particles are called gauge bosons.

There are four fundamental forces in nature.

have a ridiculous mass (x100 that of a proton. Not photon. But proton!

7 These exchange particles are called gauge bosons. Gauge bosons are virtual particles, and only exist for an extremely short amount of time. There are four fundamental forces in nature. Gravity s crap, so no one s really bothered about it, but here s the rest: The W bosons have a ridiculous mass (x100 that of a proton. Not photon. But proton!), which results in a very short range. Because of this ridiculous mass, creating a W boson uses so much energy, it can only exist for a short time and can t travel that far as a result.

8 This works vice versa with photons, which have absolutely no mass, so as a result, we get an infinite range. Feynman Diagrams Because particle interactions can be a proper bitch, a nice way to express them is through Feynman diagrams (as opposed to doing like deadly calculations). There are some rules though obviously: - Incoming particles start at the bottom, and move upwards (time moves upwards) - Baryons and leptons can t cross from one side to the other - Charges on both sides must balance - Gauge bosons are represented by wiggly lines (yes, this is the proper technical term) - All other particles are represented by straight lines Electromagnetic Repulsion Electron Capture

Beta-minus & Beta-plus Decay Quarks Don t listen to any of the bollocks chemists tell you, quarks are fundamental particles, and are the building blocks for hadrons, and consequently, antibaryons and

9 Beta-minus & Beta-plus Decay Quarks Don t listen to any of the bollocks chemists tell you, quarks are fundamental particles, and are the building blocks for hadrons, and consequently, antibaryons and antimesons are made from antiquarks. The 3 we need to know about, are the up, down, and strange quarks (and their respective antiquarks) Baryons As we know, baryons are made up of 3 quarks. Here s how:

Mesons Pions are just made of up, down, anti-up, and anti-down quark combinations. Kaons, however, have strangeness, so they do contain strange and anti-strange quarks.

10 Mesons Pions are just made of up, down, anti-up, and anti-down quark combinations. Kaons, however, have strangeness, so they do contain strange and anti-strange quarks. Strangeness Strangeness is a property that the strange quark has, and is a quantum number like baryon and lepton number. Unlike the baryon number and lepton number, strangeness is not always conserved. It s only conserved in the strong interaction. And of course, their corresponding anti particles have the complete opposite values. The Lone Quark No you cannot get a quark on its own.

11 The Photoelectric Effect If you shine (bright like a diamond) light of a high enough frequency onto the surface of a metal, electrons shall be emitted. How this is works, is that the free electrons on the surface of the metal absorbs the energy from the light, and if enough is absorbed, the electron is released. This is what is known as the photoelectric effect, and the emitted electrons are called photoelectrons. The key points here are: - For a given metal, no photoelectrons are emitted if the photon is below the threshold frequency - Photoelectrons have a range of kinetic energy from 0 to a max value, which increases with the frequency of the radiation and is not affected by the intensity - The amount of photoelectrons emitted per second is affected by the intensity Initially, the photoelectric was attempted to be explained by wave theory, but it just couldn t. Einstein s Photon Model of Light made much more sense. He suggested that EM waves and their energy exist in discrete packets, which we know as, photons. He saw these photons of light as having a 1-on-1, particle-like interaction with an electron in a metal surface. A photon would transfer all of its energy to a specific electron. Before an electron can be emitted, it needs enough energy to break the forces holding it there. This is called the work function and the value of the work function depends on the metal (\m/). Photon Emission Energy Levels Ionisation: The process of creating ions. Ionisation Energy: Amount of energy required to completely remove an electron from an atom in its ground state - Electrons in an atom can only exist in certain energy levels with n = 1 being ground state - Electrons can move up/down energy levels - An atom in anything past ground state is in an excited state

12 Excitation by Collision When an electron in an atom is hit by an electron with enough energy (has to be the exact amount required, no less, no more) in order to move it to a higher energy level. When it gets to a point where it s excited to the point of ionization, this is called ionisation by collision. To clarify, the collision isn t actually a real collision, the electrons don t actually touch, they just go near each other and repel, but for argument s sake we call it a collision. Excitation by Absorption Here, instead of being transferred energy by a colliding electron, an electron is excited by instead absorbing energy from a photon. Once again, has to be exact.

De-excitation And obviously the opposite of excitation. An electron can drop from a very high energy state to ground state and as a result give off a photon equal to the energy difference.

13 De-excitation And obviously the opposite of excitation. An electron can drop from a very high energy state to ground state and as a result give off a photon equal to the energy difference. An electron being de-excited from any level to any level will give off a photon, its energy will just depend on the difference. Filament Tube Lighting Arguably the most defining factor of any classic Pakistani household, the human race, especially the brown members of it, love filament tube lighting. As a brown man, and a scientist, I find them especially amazing, and it s because of how they work: - The filament is heated and electrons are released as a result - A voltage is applied to the ends of the tube which causes them to accelerate - Electrons collide with the low pressure gas (whatever that may be), causing excitation - Once they de-excite, photons are emitted corresponding to the energy change (UV in this case) - The phosphorus coating then absorbs the photons and those atoms are then excited - The phosphorus atoms de-excite and a photon is emitted corresponding to the energy change (visible light in this case) Spectra A continuous spectra contains all possible wavelengths - There are no gaps in a continuous spectrum - Spectrum of white light is continuous - Hot objects emit a continuous spectrum in the visible and infrared A line spectra contains only lines of the wavelengths emitted. - Produced by white light through a cool gas - Produced by an excited gas - Different elements produce unique patterns of line spectra

$Here s how we prove light has dual nature: On the one hand it s obviously a wave, and we know this because light diffracts.$ But we also know it s a particle, thanks to the photoelectric effect, as an electron absorbs all the energy in a light photon.

But we also know it s a particle, thanks to the photoelectric effect, as an electron absorbs all the energy in a light photon.

$oppositely charged magnetic field. But we also know it s a wave, as electrons diffract too.$

14 Wave-Particle Duality I m so sorry to fuck with your mind like this, but everything is a wave and a particle. And there s proof behind it. Here s how we prove light has dual nature: On the one hand it s obviously a wave, and we know this because light diffracts. But we also know it s a particle, thanks to the photoelectric effect, as an electron absorbs all the energy in a light photon. We can also prove electrons have dual nature: On the one hand it s obviously a particle, and we know this because they can be deflected by an oppositely charged magnetic field. But we also know it s a wave, as electrons diffract too. De Brogile All this crazy crap was hypothesized by a man of the name Louis de Brogile (what a legend). As you could guess, he was the man behind the de Brogile wavelength which relates a wave property to a moving particle property (momentum):

Particles. Constituents of the atom

Particles. Constituents of the atom Particles Constituents of the atom For Z X = mass number (protons + neutrons), Z = number of protons Isotopes are atoms with the same number of protons number but different number of neutrons. charge Specific