Atomic Structure PmT

• An atom is formed of 3 constituents: protons, neutrons and electrons.
• The nucleus of an atom is formed of protons and neutrons, therefore they are known as nucleons.
• The specific charge of a particle is calculated by dividing a particle’s charge by its mass.
• The proton number is the number of protons in an atom and is denoted by 'p'.
• Knowledge and understanding of any scientific concept changes over time in accordance to the experimental evidence gathered by the scientific community.
• Scientists did not always agree that matter had this wave-particle duality, however as time went on and experimental evidence for this phenomena was gathered (notably electron diffraction and the photoelectric effect), it was eventually accepted.
• These pieces of experimental evidence must first be published to allow them to be peer-reviewed by the community to become validated, and eventually accepted.
• The Z nucleon number is the number of protons and neutrons, denoted by 'Z'.
• Isotopes are atoms with the same number of protons but different numbers of neutrons.
• The strong nuclear force (SNF) keeps nuclei stable by counteracting the electrostatic force of repulsion between protons in the nucleus, and acts only on nucleons with a very short range, where it is attractive up to separations of 3 fm, but repulsive below separations of 0.5 fm.
• Unstable nuclei are those which have too many of either protons, neutrons or both, causing the SNF to not be enough to keep them stable, and these nuclei will decay in order to become stable.
• The nucleon number decreases by 4.
• For every type of particle there is an antiparticle which has the same rest energy and mass but all its other properties are opposite the particles.
• A good example to think about to describe repulsion, is to imagine an exchange as a heavy ball being thrown from one person to another, as the ball is thrown it carries momentum to the second person causing them to move back.
• This same principle can be applied to describe attraction, but instead of a heavy ball, the exchange particle is a boomerang.
• There are four fundamental forces: gravity, electromagnetic, weak nuclear and strong nuclear.
• Exchange particles carry energy and momentum between the particles experiencing the force and each fundamental force has its own exchange particles.
• All particles are either hadrons or leptons.
• The energy of photons is directly proportional to the frequency of electromagnetic radiation, as shown in the equation: E = hc = λ.
• The positron is the antiparticle of the electron, and an electron antineutrino is the antiparticle of a neutrino.
• Annihilation is where a particle and its corresponding antiparticle collide, as a result their masses are converted into energy.
• Forces between particles are caused by exchange particles.
• This energy, along with the kinetic energy of the two particles is released in the form of 2 photons moving in opposite directions in order to conserve momentum.
• Pair production is where a photon is converted into an equal amount of matter and antimatter.
• Pair production can only occur when the photon has an energy greater than the total rest energy of both particles, any excess energy is converted into kinetic energy of the particles.
• Leptons are fundamental particles, meaning they cannot be broken down any further, and they do not experience the strong nuclear force.
• The weak nuclear force is responsible for beta decay, electron capture, and electron-proton collisions, all of which can be represented as the particle interaction diagrams below.
• Electromagnetic radiation travels in packets called photons, which transfer energy and have no mass.
• Each electron can absorb a single photon, therefore a photoelectron is only emitted if the frequency is above the threshold frequency.
• The photoelectric equation is , and it shows the relationship hf E = Φ + E k (max) between the work function, maximum kinetic energy and the frequency of light.
• Electrons in atoms can only exist in discrete energy levels, and these electrons can gain energy from collisions with free electrons, which can cause them to move up in energy level, this is known as excitation, or they can gain enough energy to be removed from the atom entirely, this is called ionisation.
• Beta-plus decay is also a change of charge where a neutron changes into a proton, a down quark changes into an up quark, and the change in baryon number, electron lepton number, muon lepton number, and strangeness is zero.
• If the intensity of the light is increased, if the frequency is above the threshold, more photoelectrons are emitted per second.
• The stopping potential is the potential difference you would need to apply across the metal to stop the photoelectrons with the maximum kinetic energy.
• Ionisation occurs if the energy of the free electron is greater than the ionisation energy.
• The threshold frequency couldn't be explained by the wave theory, as it suggests that any frequency of light should be able to cause photoelectric emission as the energy absorbed by each electron will gradually increase with each incoming wave.
• An example of a practical use of excitation is in a fluorescent tube in order to produce light.
• The photoelectric effect could be explained by the photon model of light which suggested that EM waves travel in discrete packets called photons, each with an energy which is directly proportional to frequency.
• The work function of a metal is the minimum energy required for electrons to be emitted from the surface of a metal, and it is denoted by ϕ.
• If an electron becomes excited, it will quickly return to its original energy level (the ground state), and therefore release the energy it gained in the form of a photon.