Atomic structure

• Give two ways that an atoms electron arrangement can be changed

  1. Absorbing electromagnetic radiation
  2. Emitting electromagnetic radiation
• Explain how an atoms electron arrangement changes when it absorbs EM raidiation

  ● Electrons move further away from the nucleus

  ● They move to a higher energy level
• Explain how an atoms electron arrangement changes when it emits EM radiation

  ● Electrons move closer to the nucleus

  ● They move to a lower energy level
• What do all forms of the same element have in common?

  They all have the same number of protons
• What is the name given to the number of protons in an atoms?

  Atomic number
• What is an atoms mass number?

  The total number of protons and neutrons in an atom's nucleus.
• What is an isotope of an atom?

  Atoms of the same element with different numbers of neutrons, but the same number of protons
• How do atoms turn into positive ions?

  ● They lose one or more of their outer electrons

  ● Electrons are negatively charged, so the resultant charge of the atom is positive
• How did the plum pudding model describe the atom?

  A ball of positive charge, with negatively charged electrons distributed evenly throughout it.
• Prior to the discovery of the electron what was believed about the atom?

  The atom was believed to be indivisible
• Which experiment lead to the plum pudding model being discard

  Rutherford alpha scattering experiment
• What is the name given to the currently accepted model of the atom?

  The Bohr nuclear model.
• State the conclusions of the Alpha-Scattering experiment

  ● Most of the mass of the atom is concentrated at the centre in the nucleus

  ● The nucleus is positively charged
• What reinforces a scientific theory

  When experimental results agree with the hypothesised theoretical calculations and theories
• What did James Chadwick’s experiments on the atom prove?

  The existence of neutrons
• Why do unstable nuclei give out radiation?


  ● Unstable nuclei undergo decay to become more stable

  ● As they release radiation their stability increases
• What is the name of the process in which an unstable nucleus gives out radiation to become more stable?


  Radioactive decay
• Define the activity of an unstable nucleus

  Activity is the rate of decay of a source of unstable nuclei
• What is the unit of radioactive decay?

  Becquerel (Bq)
• What is the count?

  The number of radioactive decays per second for a radioactive source
• Give an example of a detector that may be used to measure count rate?

  Geiger-Muller tube
• State 4 types of nuclear radiation

  1. Alpha particles
  2. Beta particles
  3. Gamma rays
  4. Neutrons
• What are the constituents of an alpha particle?

  ● Two protons and two neutrons

  ● It is the same as a helium nucleus
• What is the range of an alpha particle through air?

  A few centimetres (normally in the range of 2-10cm).
• What will stop beta radiation from passing through a point?

  ● A thin sheet of aluminium

  ● Several metres of air
• What will stop gamma radiation from passing through a point?

  ● Several centimetres of lead

  ● A few metres of concrete
• Which type of radiation is most ionising?

  Alpha radiation
• Which type of radiation is least ionising?

  Gamma rays
• State any changes to mass or charge that occur due to the emission of a gamma ray.

  Both mass and charge remain unchanged.
• Describe the nature of radioactive decay.

  ● Random

  ● Which nuclei decays and when is determined only by chance

  ● It is impossible to predict which nuclei will decay and when
• Define the half-life of a radioactive isotope.

  ● The time it takes for the number of unstable nuclei in a substance to halve

  ● The time it takes for the count rate from a sample to fall to half its initial level
• What is radioactive contamination?

  The presence of unwanted radioactive nuclei on other materials.
• What is irradiation?

  ● The process of exposing a material to nuclear radiation

  ● The material does not become radioactive
• Why is it important for the results of studies on the effects of radiation to be published and shared with other scientists?

  ● To allow the findings to be independently checked

  ● This is known as peer review
• Give 4 sources of background radiation?

  1. Rocks
  2. Cosmic rays from space
  3. Nuclear weapon testing
  4. Nuclear accidents
• How should background radiation be dealt with in calculations?

  The background count should be subtracted from any readings before calculations (half life etc.) are attempted.
• What is the unit used to measure radiation dosage?

  Sieverts (SV)
• How many millisieverts equal 1 sievert?

  1000 millisieverts = 1 sievert
• Why might the radiation dosage that different people experience differ?

  ● Some occupations involve working with radiation

  ● Background radiation differs with location due to things such as the locality of nuclear power stations or radiation related testing
• What factor determines how dangerous a particular radioactive isotope is?

  The half-life of the isotope