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Atomic Structure and Radioactivity: A Comprehensive Guide for High School Students, Cheat Sheet of Physics

Physics

A comprehensive overview of atomic structure and radioactivity, covering key concepts such as atomic models, isotopes, radioactive decay, and the effects of radiation. It includes detailed explanations, diagrams, and examples to enhance understanding. Suitable for high school students studying chemistry or physics.

Typology: Cheat Sheet

2024/2025

Uploaded on 01/20/2025

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billy-bobmcgee 🇬🇧

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Relative Electrical Charges of Subatomic Particles
• In the centre of every atom there is a nucleus which contains protons and neutrons.
• Atomic number: the number of protons in an atom of an element.
• All atoms of a particular element have the same number of protons.
Particle
Relative charge
Relative mass
Proton
+1
1
Neutron
0
1
electron
-1
Very small, 0 or 1
1836
• An atom has an overall charge of 0, so the number of protons = number of electrons
Why doesn’t an atom have charge?
• Relative electrical charge
− Electrons: -1, protons :+1
• No of electrons = no of protons
Atom radius = 0.1 nm (1* 10-10 m)
Nucleus radius = 1
10000 of an atom (1 * 10-14m)
Formulae
• Number of neutrons = mass number – atomic number = 19 – 9 = 10
• Atomic number = number of protons = 11
• Mass number = protons + neutrons
Ionization
• Sometimes outermost electrons absorbs excessive energy causing the electron to completely
leave the atom
• More positive charges will remain in the atom than negative charges.
• As a result, atom will become a positive ion.
Ionizing radiation: able to knock electrons off = ionize them
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Download Atomic Structure and Radioactivity: A Comprehensive Guide for High School Students and more Cheat Sheet Physics in PDF only on Docsity!

Relative Electrical Charges of Subatomic Particles

  • In the centre of every atom there is a nucleus which contains protons and neutrons.
  • Atomic number: the number of protons in an atom of an element.
  • All atoms of a particular element have the same number of protons. Particle Relative charge Relative mass Proton +1 1 Neutron 0 1 electron - (^1) Very small, 0 or 1 1836
  • An atom has an overall charge of 0, so the number of protons = number of electrons Why doesn’t an atom have charge?
  • Relative electrical charge − Electrons: - 1, protons :+
  • No of electrons = no of protons Atom radius = 0.1 nm (1* 10-^10 m) Nucleus radius = 1 10000 of an atom (1 * 10-^14 m) Formulae
  • Number of neutrons = mass number – atomic number = 19 – 9 = 10
  • Atomic number = number of protons = 11
  • Mass number = protons + neutrons Ionization
  • Sometimes outermost electrons absorbs excessive energy causing the electron to completely leave the atom
  • More positive charges will remain in the atom than negative charges.
  • As a result, atom will become a positive ion. Ionizing radiation : able to knock electrons off = ionize them

Relative Atomic Mass

Relative atomic mass = sum of (isotope adundance × isotope mass no) 100 (total no at atoms)

  • Isotopes: atoms of the same element with different numbers of neutrons/mass numbers but same number of protons/atomic number.
  • Relative atomic mass: an average value that takes account of the abundance of the isotopes of the element High relative atom mass
  • Less waste products
  • Less pollutant

Electronic Structure

Electrons in an atom are arranged in energy levels/shells Shells gets further away from nucleus – increase in energy levels Electrons can gain electromagnetic radiation Electron moves further from nucleus To a higher energy level Though soon electron will fall back to the lower/original energy level Re-emitting energy as electromagnetic radiation Explain why fluorine and chlorine are in the same group of the period table. Give the electronic structures of fluorine and chlorine in your explanation. (2)

  • The electronic structure of fluorine is 2,7 and chlorine is 2,8,
  • F & Cl both has 7e- in outer shell Explain why 𝟔𝑪 𝟏𝟐 and 𝟔𝑪 𝟏𝟒 are isotopes of carbon. You should refer to the numbers of sub- atomic particles in the nucleus of each isotope. (3)
  • Isotope is different forms of the same element, which have the same no of protons but different no of neutrons
  • They both have 6 protons
  • 12C has 6 neutrons, 14C has 8 protons

Niels Bohr adapted the nuclear model by suggesting electrons orbited the nucleus at specific distance. Explain how the distance at which an electron orbits the nucleus may be changed. (3)

  • Electrons may absorb electromagnetic radiation and move further form nucleus to a higher energy level.

Radioactivity

Background Radiation – radiation that is always present around us in the environment eg soil, rocks Detecting Radiation Geiger-Muller (GM) tube – detect alpha, beta & gamma radiation

  • Ratemeter – gives a reading in counts per second
  • Scaler – counts total number of particles / burst of gamma radiation
  • Amplifier/loudspeaker – makes ‘click’ when each particles / bursts of gamma radiation detected
  1. Particles pass through the thin mica ‘window’
  2. They ionised the gas inside → set off high-voltage spark & conduct electric current
  3. When radiation from radiation source measured, reading includes background radiation Cloud chamber
  4. Chamber has cold alcohol vapour in the air inside it
  5. Alpha particles makes vapour condense → can see trails of droplets where each particle passes through
  6. Vacuum Tube : Allows electrons to move freely.
  7. Electron Gun : Shoots electrons (cathode rays).
  8. Anode : Accelerates electrons towards the screen.
  9. Deflection System : Guides electron beam to specific points.
  10. Fluorescent Screen : Glows where electrons hit, forming images.

Characteristics of Emission

Nuclear radiation

Alpha, Gamma & Beta Radiation

  • Most isotopes are unstable.
  • Unstable isotopes can undergo radioactive decay emitting radiation to become more stable.
  • Radioactive material: Consists of unstable isotopes that can decay
  • Decay: Rot or decompose through the action of bacteria and fungi. 4 types of nuclear radiation: Alpha & Beta particle, Gamma Rays & Neutrons. Alpha particles Beta Particles Gamma rays Description Each particle is 2 protons + 2 neutrons (Helium nucleus) Each particle is an electron (created when nucleus decays) Electromagnetic waves- nucleus gets rid of extra energy Relative charge +2 - 1 0 Mass High compared with β Low - Speed 0.1 × speed of light Slower → speed more time close to any e- they pass 0.9 x speed of light Speed of light Ionising effect Strong Coz have greater charge & size → exert more force on e-^ knocking em off Weak Very weak Penetrating effect Not very penetrating Stopped by a thick sheet of paper, or by skin, or by few cm of air Penetrating Stopped by few mm of aluminium or other metals Very penetrating Never completely stopped Effect of fields +2 charged → equivalent to electric current → deflect by magnetic & electric fields
  • 1 charged, light → deflected more in opposite direction Uncharged → not deflected by magnetic & electric fields Neutron: Nucleus with excessive neutrons = unstable, emits a neutron to increase stability Penetrating effect Effects of fields

Radioactive Decay

Radioactive decay

  • If an isotope is radioactive (becomes radioisotopes), it has unstable nuclei (neutrons & protons)
  • Unstable nucleus disintegrates and emit particles (& sometimes wave energy – gamma radiation)
  • When they emit alpha & beta particles − Makes nucleus more stable − Change number of neutrons & protons − Decay into atoms of different elements Alpha decay by alpha emission Alpha particles consists of 2 proton and 2 neutron When an alpha particle is emitted from nucleus
  • Nucleus loses 4 nucleons → mass no ↓
  • Nucleus loses 2 protons → atomic no ↓ Beta decay by beta emission Mass number remains unchanged Atomic number increases by 1 When it’s emitted
  • Neutron changes into proton since 𝛽𝛽 is - 1 charged & no e- inside nucleus
  • e- emitted at high speed as 𝛽𝛽-particle is also created to balance +ve charged of protons
  • An uncharged, almost massless antineutrino is created A – mass number Z – atomic number Emitted alpha particle (helium nucleus) With mass number – 2 And atomic number - 2
  • It is suitable because it will not need to be replenished, and its weak activity means it won’t be harmful to anyone. State two of the social, economic or environmental issues involved in the storage of radioactive materials with very long half-lives (2) Social Economic Environmental
  • Cause cancer
  • Local objections
  • Ppl move away
  • High cost of storage
  • Reduction of tourism/land
  • Crop mutation
  • Leakage into water supplies
  • Pollution of atmosphere/water supply Net Decline
  • Calculate the ratio of net decline of radioactive nuclei after X half-lives
  • Half the initial number of nuclei, and keep doing so X number of times Net decline = 𝐢𝐧𝐢𝐭𝐢𝐚𝐥 𝐧𝐮𝐦𝐛𝐞𝐫−𝐧𝐮𝐦𝐛𝐞𝐫 𝐚𝐟𝐭𝐞𝐫 𝐗 𝐡𝐚𝐥𝐟 𝐥𝐢𝐯𝐞𝐬 𝐢𝐧𝐢𝐭𝐢𝐚𝐥 𝐧𝐮𝐦𝐛𝐞𝐫

Harmfulness Of Radiation

Contamination – radioactive particles get onto other objects

  • Lasts for a long period of time
  • The source of the radiation is transferred to an object
  • Radioactive contamination is the unwanted presence of radioactive atoms on other materials – the hazard is the decaying of the contaminated atoms releasing radiation – irradiating you
  • E.g. radioactive dust settling on your skin (your skin becomes contaminated) Irradiation – process by which objects are exposed to radiation (ionizing & non ionizing radiation)
  • Lasts only for a short period of time
  • The source emits radiation, which reaches the object
  • Exposing an object to nuclear radiation, but does not make it radioactive
  • E.g. radioactive dust emitting beta radiation, which “irradiates” your skin
  • Medical items are irradiated sometimes to kill bacteria on its surface, but not to make the medical tools themselves radioactive Ionizing radiation
  • Ionization radiation is very dangerous as it can enter living cells and interact with the molecules inside.
  • Can ionize DNA causing mutation, which in rare cases can cause uncontrollable cell division = cancer, UV can also cause cancer though not ionizing Despite harmfulness of radioactive particles, orders, from alpha to radio waves it can vary depending on the location of the source − When source is external, alpha particles isn’t harmful as they are lowly penetrating hence can’t penetrate our skin − Since beta and gamma is most penetrating its most dangerous as external source − In internal source, alpha particles is most dangerous due to ionization Harmfulness of radiation also depends on the “dosage”/amount of radiation, one is exposed to, which relies on 3 factors:

Explain how the risk from internal contamination is different to the risk of external irradiation by a source of alpha radiation. (5)

  • alpha radiation has a low penetrating ability (so externally) alpha radiation is stopped by skin (so is low risk)
  • internally, alpha radiation is absorbed by living tissue / organs (as) alpha radiation is highly ionising (internal) contamination will cause greater (risk of) harm to cells / tissues / organs / DNA / genes

Nuclear Fission & Fusion

For fission to start, an unstable nucleus must first absorb an initial neutron. This neutron provides extra energy to overcome the nucleus's stability, giving it a “kick” to initiate splitting. Nuclear fission is the splitting of a large, unstable nucleus (e.g., uranium or plutonium) into two smaller nuclei, releasing energy in the process. Spontaneous vs. Induced Fission :

  • Spontaneous fission is rare. Typically, fission occurs only after the unstable nucleus absorbs a neutron. Fission Process:
  • When the unstable nucleus absorbs a neutron, it splits into two smaller, roughly equal-sized nuclei known as "daughter nuclei."
  • During the split, the nucleus releases: − Two or three neutrons − Gamma rays − Energy (primarily in the form of kinetic energy in the daughter nuclei and emitted neutrons)
  • The emitted neutrons may collide with other radioactive nuclei, causing them to absorb neutrons and become unstable.
  • This newly unstable nucleus then splits, releasing more neutrons and energy.
  • This sequence continues as a chain reaction where each fission event can initiate further events.
  • If the chain reaction is uncontrolled, it will grow exponentially, which is the principle behind a nuclear weapon. Nuclear Reactors
  • In nuclear reactors, the rate of fission must be carefully controlled to prevent the reaction from becoming unmanageable.
  • Control rods are used to absorb excess neutrons and slow down the reaction, which helps keep the fission process stable.
  • The energy released from fission is used to heat water, turning it into steam that drives turbines connected to an electricity generator. Advantages Disadvantages
  • The fuel (uranium or plutonium) is relatively cheap.
  • Nuclear fission produces a large, steady amount of energy.
  • Although not renewable, nuclear energy is considered clean since it does not produce greenhouse gases like fossil fuels.
  • Nuclear power plants are very expensive to build.
  • Disposal of nuclear waste is costly and requires special bunkers for safe storage underground.
  • There is a risk of a major disaster if the plant malfunctions, which, although unlikely, raises public concern and suspicion about nuclear energy. Nuclear Fusion
  • This is when two small nuclei fuse to form a heavier nucleus, releasing (lots of) energy
  • The sum of the masses of the two nuclei is more than the mass of the heavier nucleus
  • Some of the mass is converted into energy. (released as radiation) E = MC^2 – mass * speed of light squared
  • The sun is a natural fusion reactor. Also creates element heavier than hydrogen in stars.
  • Fusion would be a much more efficient way of producing energy compared to fission
  • Fusion requires extremely high temperatures and pressures (around 10 million degrees Celsius) to overcome the repulsive forces between nuclei.
  • Currently, these conditions are achievable only in stars, so scientists are conducting experimental research to find a way to make fusion possible on Earth with positive net energy output.