Atomic structure

• What is the radius of an atom?

  1 x 10-10 m
• What are the electric charges of electrons and protons?

  protons- +1

  electrons- -1
• An atoms nucleus makes up less that 1/____ of the radius of the atom?

  10000
• When does the energy level of an electron change?

  when an atom emits or absorbs EM radiation
• What effect does emitting and absorbing EM radiation have an electrons energy level?

  ABSORB- moves electrons to a HIGHER energy level (further from nucleus)

  EMITTED- when an electron drops to a lower energy level
• Do an atom become a positive or negative ion when it loses electrons?

  Positive
• The number of _____ is different in isotopes?

  neutrons
• What are isotopes?

  atoms of the same element with different numbers of neutrons.
• Who discovered electrons?

  J.J Thompson, in 1897
• What is the plum pudding model?

  a ball of positive charge with with electrons embedded in it
• In Rutherfords and Marsdens experiment some alpha particles were deflected, what did this mean about the atom?


  • must have been repelled by same charge of alpha particles
  • the repelling charge must have been heavier than alpha particle, otherwise they would have passed through
• What happened in Rutherford and Marsdens experiment?

  alpha particles were fired at a piece of thin gold foil
• What did the alpha particle experiment lead to conclude about the atom?

  • mass of atom is concentrated in a central positively charged nucleus
  • electrons surround this nucleus
• What did Bohr suggest? (hint: he adapted the nuclear model)

  electrons orbit nucleus at specific distances (energy levels)
• What did Chadwick discover?

  the neutron
• In which order were protons, neutrons and electrons discovered?

  1. 1897- electron
  2. 1909- proton
  3. 1932- neutron
• Why do unstable nuclei give out radiation?

  to become more stable
• Atomic decay is a ______process?

  random
• What is the activity of a radioactive source?

  the rate at which it decays
• What is activity rate measured in?

  Becquerels (Bq). **1 Bq = 1 decay (or count) per second
• What is the count rate?

  number of decays recorded each second by a detector (e.g. Geiger Muller tube)
• Give the ionising power of each type of nuclear radiation?

  Alpha: strong Beta: reasonable Gamma: poor
• By what material is each type of nuclear radiation stopped by?

  alpha- paper

  beta- thin aluminium

  gamma- thick lead
• What is alpha radiation? (Think particles)

  two neutrons and two protons (helium nucleus)

  ejected from the nucleus
• What are hazards of alpha radiation?

  highly likely to be absorbed and cause damage if passing through living cells
• What is beta radiation?

  high speed electron ejected from nucleus as a neutron turn into a proton
• What are the hazards of beta radiation?

  likely to cause damage if absorbed by living cells

  can penetrate body to inner organs
• What is gamma radiation?

  EM radiation

  emitted from nucleus
• Are there hazards of gamma radiation?

  no really, likely to pass through living cells without being absorbed or causing ionisation
• What is the fourth type of radiation?

  neutron
• What is radioactive contamination?

  the unwanted presence of materials containing radioactive atoms on other materials
• What is irradiation?

  Exposing an object to nuclear radiation (object doesn’t become radioactive)
• How can we protect against unwanted irradiation?

  1. using sources of lowest activity for shortest time possible
  2. wear protective clothing- e.g. lead apron
  3. don’t handle sources with bare hands
• What is the half life?

  average time it takes for half the nuclei to decay
• Does the half-life of a particular radioactive isotope change?

  No.
• are Isotopes with are short half life stable/unstable?

  unstable
• Do isotopes with a short and long half-life emit radiation quickly or slowly?

  SHORT- quickly- exposure very hazardous

  LONG- slowly- exposure less hazardous
• What are some uses of nuclear radiation?

  smoke detectors, medical tracers
• How can radioactive isotopes be used in medical tracers?

  to look at internal organs

  isotope ingested, as it travel around the body it can be detected on the outside
• How can isotopes be used to monitor kidney function?

  isotope will pass through kidneys, if it builds up in one kidney it suggest it isn’t working efficiently.