topic 4- atomic structure

• What is the charge of the nucleus?

  Positively charged
• What particles are found in the nucleus?

  Neutrons and protons
• What is the charge of electrons?

  Negatively charged
• What is the relative mass of a proton?

  1
• What is the relative charge of a neutron?

  0
• What is the relative mass of an electron?

  0 (0.0005)
• What is the typical radius of an atom?

  $1 \times 10^{-10} \text{ metres}$
• How much smaller is the nucleus compared to the atom?

  10,000 times smaller
• Where is most of the mass of the atom concentrated?

  At the nucleus
• What is the arrangement of electrons in an atom?

  • Electrons lie at different distances from the nucleus
  • They occupy different energy levels
  • Arrangements change with interaction with EM radiation
• What do all atoms of the same element have in common?

  Same number of protons
• What defines a neutral atom?

  Same number of electrons and protons
• What are isotopes?

  Atoms of the same element with same protons but diffrent neutrons
• What happens if there are more electrons than protons?

  The atom has a negative charge
• What happens if there are fewer electrons than protons?

  The atom has a positive charge
• What does the number of protons in an element indicate?

  It does not change for that element
• How do electrons interact with EM radiation?

  • Electrons can change orbit
  • Moving to a higher orbit absorbs EM radiation
  • Falling to a lower orbit emits EM radiation
• What occurs when an electron gains enough energy?

  It can leave the atom, forming a positive ion
• What did Dalton propose about atoms in 1800?

  Everything was made of tiny spheres (atoms)
• Who discovered the electron in 1897?

  JJ Thomson
• What was the Plum Pudding Model?

  Electrons dispersed in positive "pudding"
• What did Rutherford discover in 1911?

  Most of the atom was empty space
• What did the Gold Foil Experiment demonstrate?

  Most alpha particles went straight through
• What did slight deflections of alpha particles indicate?

  The nucleus must be charged
• What did large deflections of alpha particles suggest?

  The nucleus contains most of the mass
• What did Bohr produce in 1913?

  The final model of the atom
• What did Chadwick prove about the nucleus?

  Neutrons existed in the nucleus
• What is radioactive decay?

  • A random process
  • Nucleus gives out radiation to become stable
• What is activity in radioactive decay?

  Rate of decay of unstable nuclei
• How is activity measured?

  In Becquerel, Bq
• What is count-rate?

  Number of decays recorded per second
• What are the forms of radioactive decay?

  • Alpha (α): Highly ionising, weakly penetrating
  • Beta Minus (β): Medium ionising, medium penetration
  • Gamma (γ): Low ionising, highly penetrating
  • Neutrons: Not specified
• What is alpha decay?

  Emission of a helium nucleus
• What is the ionising power of alpha particles?

  Highly ionising
• What is the penetration power of alpha particles?

  Weakly penetrating (~5cm of air)
• What is beta minus decay?

  Emission of an electron
• What is the ionising power of beta particles?

  Medium ionising
• What is the penetration power of beta particles?

  Medium penetration (~50cm of air, paper)
• What is gamma decay?

  Emission of gamma radiation
• What is the ionising power of gamma radiation?

  Low ionising