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 an atom concentrated?

  At the nucleus
• How do electrons arrange themselves around the nucleus?

  • Electrons lie at different distances from the nucleus
  • They occupy different energy levels
  • Arrangements change with EM radiation interaction
• 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 with same protons, different neutrons

  
• What does the symbol $Z$ represent in isotopes?


  Proton number
• What does the symbol $A$ represent in isotopes?


  Mass number
• What does the symbol $N$ represent in isotopes?


  Charge
• What happens to an atom when it gains enough energy?

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

  Atoms are tiny spheres that cannot be divided
• Who discovered the electron in 1897?

  JJ Thomson
• What was the Plum Pudding Model?

  • Proposed by JJ Thomson
  • Atoms consist of a positive "pudding"
  • Negative electrons are dispersed throughout
• What did Rutherford discover about the atom in 1911?

  Most of the atom is empty space
• What happens to alpha particles that are slightly deflected?

  The nucleus must be charged
• What does it mean if alpha particles are deflected by more than 90°?

  The nucleus contains most of the mass
• What did the Gold Foil Experiment demonstrate?

  Most alpha particles pass through, indicating empty space

  
• What is the structure of the atom according to the Bohr model?

  • Positive nucleus at the center
  • Negative electrons exist in fixed orbitals
• Who provided evidence for the existence of neutrons?

  James Chadwick
• What is radioactive decay?

  • Random process
  • Unstable nuclei emit radiation to become stable
• What is activity in terms of radioactive decay?

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

  In Becquerel, Bq
• What is count-rate in radioactive decay?

  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
• What is alpha decay?

  Emission of a helium nucleus
• How penetrating is alpha radiation?

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

  Emission of an electron
• How penetrating is beta radiation?

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

  Emission of gamma radiation
• How penetrating is gamma radiation?

  Highly penetrating (very far in air)
• What are nuclear equations used for?

  • Represent radioactive decay
  • Show changes in mass and charge
• What happens during alpha decay in nuclear equations?

  Mass and charge of nucleus decrease
• What happens during beta decay in nuclear equations?

  Charge of nucleus increases, mass unchanged