1.4 atomic structure

• What is an approximation for the radius of an atom?

  1x10⁻¹⁰ metres
• What are the three subatomic constituents of an atom?

  • Proton
  • Neutron
  • Electron
• Where is most of the mass of an atom concentrated?

  In the nucleus
• Describe the arrangement of protons, neutrons, and electrons in an atom.

  • Protons and neutrons are in the nucleus
  • Electrons are in discrete energy levels around the nucleus
• What type of charge does the nucleus of an atom have and why?

  Positive charge due to protons
• How can an atom's electron arrangement be changed?

  1. Absorbing electromagnetic radiation
  2. Emitting electromagnetic radiation
• How does an atom's electron arrangement change when it absorbs EM radiation?

  Electrons move to a higher energy level
• How does an atom's electron arrangement change when it emits EM radiation?

  Electrons move to a lower energy level
• How does the ratio of electrons to protons result in an atom having no overall charge?

  Protons equal electrons, charges cancel
• 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 atom?

  Atomic Number
• What is an atom's mass number?

  Total number of protons and neutrons
• What is an isotope of an atom?

  Different number of neutrons, same protons
• How do atoms turn into positive ions?

  • They lose one or more outer electrons
  • Resultant charge is positive due to lost electrons
• What may lead to a scientific model being changed or replaced?

  New experimental evidence contradicts existing theory
• How did the plum-pudding model describe the atom?

  A ball of positive charge with electrons distributed
• What was believed about the atom prior to the discovery of the electron?

  The atom was believed to be indivisible
• Which experiment led to the plum-pudding model being discarded?

  Rutherford’s alpha-scattering experiment
• What are the conclusions of the Alpha-Scattering experiment?

  • Most mass is concentrated in the nucleus
  • The nucleus is positively charged
• What is the name given to the currently accepted model of the atom?

  The Bohr nuclear model
• What reinforces a scientific theory?

  Experimental results agree with theoretical calculations
• What did James Chadwick’s experiments on the atom prove?

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

  To become more stable through decay
• What is the name of the process where unstable nuclei emit radiation?

  Radioactive decay
• How is the activity of an unstable nucleus defined?

  It is the rate of decay of unstable nuclei
• What is the unit of radioactive activity?

  Becquerel (Bq)
• What does count-rate refer to in radioactivity?

  The number of decays per second
• What are the four types of nuclear radiation?

  • Alpha particles
  • Beta particles
  • Gamma rays
  • Neutrons
• What are the constituents of an alpha particle?

  Two protons and two neutrons
• What can stop beta radiation from passing through?

  A thin sheet of aluminium
• What can stop gamma radiation from passing through?

  Several centimetres of lead
• Which type of radiation is most ionising?

  Alpha radiation
• Which type of radiation is least ionising?

  Gamma radiation
• What changes occur to mass or charge during gamma ray emission?

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

  • Random process
  • Decay timing is determined by chance
  • Predicting decay is impossible
• What is the half-life of a radioactive isotope?

  The time for unstable nuclei to halve
• What is radioactive contamination?

  Unwanted radioactive nuclei on materials
• Why is it important to publish radiation study results?

  To allow independent verification of findings
• What is irradiation?

  • Exposing a material to nuclear radiation
  • The material does not become radioactive
• What is one source of background radiation?

  Rocks