P4- Atomic Structure

• What is the charge of the nucleus in an atom?

  Positively charged
• What particles are contained in the nucleus of an atom?

  Neutrons and protons
• What is the relative mass of a proton?

  1
• What is the relative charge of an electron?

  • 1
• What is the typical radius of an atom?

  $1 \times 10^{-10} \text{ metres}$
• How does the radius of the nucleus compare to the radius of an atom?

  The radius of the nucleus is 10,000 times smaller than that of the atom
• Where is most of the mass of an 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 may change with interaction with EM radiation
• What do all atoms of the same element have in common?

  They have the same number of protons
• What defines a neutral atom?

  A neutral atom has the same number of electrons and protons
• What are isotopes?

  Atoms of the same element with different masses due to different numbers of neutrons
• Give an example of isotopes of carbon.

  Carbon-12, Carbon-13, and Carbon-14
• In the notation $^{A}_{Z}X\pm N$, what does $X$ represent?


  The letter of the element
• In the notation $^{A}_{Z}X\pm N$, what does <latex{A}</latex> represent?


  The mass number (number of neutrons and protons)
• In the notation $^{A}_{Z}X\pm N$, what does <latex{Z}</latex> represent?


  The proton number
• What happens when an electron gains enough energy?

  It can leave the atom to form a positive ion
• Who proposed that everything was made of tiny spheres (atoms) in 1800?

  Dalton
• What did JJ Thomson discover in 1897?

  The electron
• What model was formed after the discovery of the electron?

  The Plum Pudding Model
• What did Rutherford realize about the atom in 1911?

  Most of the atom was empty space
• What experiment did Geiger and Marsden conduct?

  The Gold Foil Experiment
• What did the Gold Foil Experiment demonstrate about the atom?

  Most of the atom is empty space
• What did the Gold Foil Experiment reveal about the nucleus?

  The nucleus must be charged and contains most of the mass
• What did Bohr contribute to atomic theory in 1913?

  He produced the final model of the atom
• What did James Chadwick provide evidence for?

  The existence of neutrons
• What is radioactive decay?

  • A random process where unstable nuclei emit radiation to become more stable
  • The rate of decay is measured in activity (Becquerel, Bq)
• What is the definition of activity in the context of radioactive decay?

  The rate at which a source of unstable nuclei decays
• What is count-rate in radioactive decay?

  The number of decays recorded by a detector per second
• What are the forms of radioactive decay?

  • Alpha (α): Highly ionising, weakly penetrating (~5cm of air)
  • Beta Minus (β): Medium ionising, medium penetration (~50cm of air, sheet of paper)
  • Gamma (γ): Low ionising, highly penetrating (very far in air, few cm of lead)
• What do nuclear equations represent?

  Radioactive decay
• What happens during alpha decay?

  The mass and charge of the nucleus decrease
• What happens during beta decay?

  The mass of the nucleus does not change, but the charge increases
• What happens during gamma decay?

  There is no change in mass or charge
• What is the definition of half-life?

  The time taken for half the nuclei in a sample to decay
• How can half-life be used in radioactive decay?

  It enables the activity of a large number of nuclei to be predicted
• If 80 atoms decay to 20 in 10 minutes, what is the half-life?

  5 minutes
• What are the characteristics of short and long half-lives?

  Short half-life:

  • Less long-term risk
  • Initially very radioactive, quickly dies down

  
  

  Long half-life:

  • Remains weakly radioactive for a long time
  • Example: Americium with a half-life of 432 years
• How does Americium function in smoke alarms?

  It emits alpha particles and is weakly penetrating, ensuring safety
• What is the net decline of radioactive nuclei after X half-lives?

  • The number of nuclei is halved for each half-life
  • Formula: $N_{net\ decline} =$$N_{initial} \times \left(\frac{1}{2}\right)^{X}$
• What is the difference between contamination and irradiation?

  Contamination:

  • Lasts a long time
  • Source of radiation transferred to an object

  
  

  Irradiation:

  • Lasts a short time
  • Source emits radiation but does not make the object radioactive