Atomic structure

• Who was the Greek philosopher that first proposed the idea of atoms?

  Democritus
• What did Democritus believe matter was made up of?

  Identical lumps called "atomos"
• In what year did John Dalton propose his atomic theory?

  1804
• How did Dalton's view of atoms differ from Democritus's?

  Dalton believed each element was made up of a different type of atom
• What did J.J. Thomson discover in his experiments?

  Electrons
• What was the plum pudding model proposed by Thomson?

  Atoms are spheres of positive charge with negative electrons embedded in them
• What experiment did Rutherford's lab conduct in 1909?

  The alpha scattering experiment
• What did Rutherford's alpha scattering experiment reveal about the atom?

  Most of the mass is concentrated in a tiny nucleus
• How did the results of the alpha scattering experiment contradict the plum pudding model?

  Some alpha particles were deflected back, which the plum pudding model couldn't explain
• What is the current model of the atom based on Rutherford's findings?

  A positively charged nucleus surrounded by a cloud of negative electrons
• Who proposed that electrons orbit the nucleus at certain distances?

  Niels Bohr
• What did James Chadwick prove in 1932?

  The existence of the neutron
• What is the relative charge of a proton?

  +1
• What is the radius of an atom approximately?

  About \(1 \times 10^{-10}\) m
• What happens to an atom when one or more outer electrons leave?

  The atom becomes a positively charged ion
• What is the significance of the half-life in radioactive decay?

  It is the time taken for the number of radioactive nuclei to halve
• What is the definition of isotopes?

  Different forms of the same element
• What do nuclear equations represent?

  Radioactive decay using element symbols
• What happens during alpha decay?

  An atom emits an alpha particle, reducing its atomic number by 2 and mass number by 4
• How is an alpha particle represented in nuclear equations?

  As \(^{4}_{2}\text{He}\)
• What is the effect of beta decay on the nucleus?

  A neutron turns into a proton, increasing the atomic number by 1
• How is a beta particle represented in nuclear equations?

  As \(^{0}_{-1}\text{e}\)
• What do gamma rays do during radioactive decay?

  They help rid the nucleus of excess energy without changing mass or atomic number
• What is the definition of half-life in terms of activity?

  The time taken for the activity to halve
• What is background radiation?

  Low-level radiation that is around us all the time
• What are the main sources of background radiation?

  Natural isotopes, cosmic rays, and human activity
• What are the key components of the current model of the atom?

  • A tiny nucleus containing protons and neutrons
  • Protons have a +1 charge, neutrons have a 0 charge
  • A cloud of negative electrons surrounding the nucleus
  • Most of the atom is empty space
• What are the steps to calculate the final activity after two half-lives?

  1. Divide the initial activity by 2 for the first half-life
  2. Divide the result by 2 for the second half-life
  3. Calculate the final activity as a percentage of the initial activity
• What are the differences between alpha decay, beta decay, and gamma rays?

  • Alpha decay: Reduces atomic number by 2, mass number by 4
  • Beta decay: Increases atomic number by 1, mass number unchanged
  • Gamma rays: No change to atomic mass or atomic number
• What is the half-life of the substance described in the activity graph?

  2 seconds
• What are the main sources of background radiation?

  • Radioactivity of naturally occurring unstable isotopes
  • Cosmic rays from space
  • Radiation due to human activity (e.g., nuclear fallout)
• Why should background radiation be measured and subtracted from results?

  To avoid systematic errors in measurements
• What unit is used to measure radiation dose?

  Sieverts (Sv)
• What is the difference between irradiation and contamination?

  Irradiation is exposure to radiation, while contamination is the presence of radioactive particles on an object
• What is the effect of irradiation on objects?

  Objects near a radioactive source are exposed to radiation
• How can the effects of irradiation be reduced?

  By using lead-lined boxes, barriers, or remote-controlled arms
• What happens if unwanted radioactive atoms get onto an object?

  The object is said to be contaminated
• Why is contamination particularly dangerous?

  Because radioactive particles could enter the body and cause harm
• What should be used when handling radioactive sources to avoid contamination?

  Gloves and tongs
• How does the danger of irradiation and contamination vary based on radiation type?

  • Outside the body: Beta and gamma are most dangerous
  • Inside the body: Alpha is most dangerous due to localized damage
  • Beta is less damaging inside, gamma is the least damaging