(Done) Atomic structure (Paper 1) Flashcards
Describe Democritus’ idea of atoms
- All matter was made up of identical lumps called ‘Atomos’
Describe John Dalton’s idea of atoms
- Each element was made up of different types of ‘Atomos’
Describe J.J.Thomson’s idea of atoms
- Discovered electrons and that they could be removed from the atom
- Spheres of positive charge with tiny negative electrons stuck in them like fruit in a plum pudding
Describe Rutherford’s idea of atoms
- Fired alpha particles at a piece of thin gold foil
- Discovered a small positive nucleus in the centre of the atom
- Discovered that most of an atom is empty space
Describe Niels Bohr’s idea of atoms
- Electrons orbiting the nucleus do so at certain distances called energy levels
Describe James Chadwick’s idea of atoms
- There is a neutrally charged particle contained within the nucleus called neutrons
How big is the radius of the nucleus relative to the radius of the entire atom
- The radius of the nucleus is about 10000 times smaller than the overall radius of the atom
What is the rough overall radius of an atom
- 1x1^-10 metres or 0.1 nanometres
What causes electrons to move to higher energy levels
- Gaining energy by absorbing EM radiation
What causes electrons to move to lower energy levels
- Losing energy by releasing EM radiation
Define isotopes
- Atoms of an element with the same number of protons but a different number of neutrons
Name the process in which unstable isotopes attempt to become stable
- Radioactive decay
Name the types of radiation released from radioactive decay
- Alpha
- Beta
- Gamma
Define ionising radiation
- Radiation that knocks electrons off atoms, creating positive ions
Define ionising power
- How easily radiation can ionise
What are alpha particles
- Two protons and two neutrons
Features of alpha radiation
- Do not penetrate very far and are stopped quickly (absorbed by a few cm in air or a sheet of paper)
- Strongly ionising due to their size
What are beta particles
- A fast moving electron released from the nucleus after a neutron becomes a proton and an electron
Features of beta radiation
- Moderately ionising
- Penetrate moderately far into materials
- Can travel a few meters in air and are absorbed by a sheet of aluminium around 5mm thick
What are gamma rays
- Waves of electromagnetic radiation released by the nucleus
Features of gamma radiation
- Penetrate far into materials
- Travels a long distance through air
- Weakly ionising as they tend to pass through instead of colliding with atoms
- Absorbed by thick sheets of lead or metres of concrete
How does beta decay affect the atomic and mass numbers
- Increases the atomic number by 1 whilst keeping the mass number the same
How does alpha decay affect the atomic and mass numbers
- Atomic number reduces by 2 and the mass number reduces by 4
How does gamma decay affect the atomic and mass numbers
- Gamma rays are a way of getting rid of excess energy from a nucleus so there is no change to the atomic or mass numbers
What is radioactivity measured by
- A Geiger-muller tube and counter records the count rate (the number of radiation counts reaching it per second
Define activity
- Rate of radioactive decay
What is activity measured in
- Becquerels (Bq)
Define background radiation
- Low level radiation that is around us all the time
List the sources of background radiation
- Radiation of naturally occurring unstable isotopes all around us
- Radiation from space know as cosmic rays
- Radiation due to human activity
Where is radiation naturally found around us
- The air
- Food
- Building materials
- Rocks
Where do cosmic rays traditionally come from
- The sun, although we are protected mostly by the atmosphere
In what form does radiation from human activity come in
- Fallout from nuclear explosions or waste
Define irradiation
- Being exposed to radiation
- Objects near a radioactive source are irradiated
Define contamination
- Unwanted radioactive atoms getting onto or into something
- If you touch a radioactive source without wearing gloves, your hands would be contaminated
How can radiation damage cells
- Radiation can enter living cells and ionise atoms or molecules within them causing tissue damage
Damage caused by low doses of radiation
- Minor damage without killing the cells
- Can give rise to mutant cells which divide uncontrollably (cancer)
Damage cause by high doses of radiation
- Kill cells completely
- Causes radiation sickness if a lot of cells get hit at once
How can high doses of radiation be used to treat cancer
- Gamma rays are directed carefully at just the right dosage to kill the cancer cells without killing any normal cells
What is nuclear fission
- A type of nuclear reaction that is used to release energy from large unstable atoms by splitting them into smaller atoms
What conditions are usually required for fission to occur
- A neutron is fired at and absorbed by the nucleus
What usually results from fission
- Two or three neutrons and two daughter nuclei of roughly the same size
How is the amount of energy from fission controlled
- Changing how quickly the chain reaction can occur through control rods which absorb neutrons
What is caused from uncontrolled fission chain reactions
- An explosion, that is how nuclear weapons work
What happens within nuclear fusion
- Two light nuclei collide at high speeds and join to create a larger, heavier nucleus
What particles are commonly used in fusion
- Hydrogen isotopes collide to form helium and energy
