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 charge of electrons?

  Negatively charged
• What is the typical radius of an atom?

  $1 \times 10^{-10} \text{ metres}$
• How much smaller is the radius of 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.
  • Their arrangement 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?

  It has the same number of electrons and protons

  
• What are isotopes?

  Atoms of the same element with different masses
• 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 $Z$ represent?


  The proton number
• What happens to the charge of an atom if there are more electrons than protons?

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

  The atom has a positive charge
• What occurs when electrons change orbit around the nucleus?

  They absorb or emit EM radiation
• What happens when electrons move to a higher orbit?

  The atom absorbs EM radiation
• What happens when electrons fall to a lower orbit?

  The atom emits EM radiation
• What can happen if 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 alpha particles went straight through, indicating empty space

  
• What did the deflection of some alpha particles in the Gold Foil Experiment suggest?

  The nucleus must be charged

  
• What did the deflection of a few alpha particles by more than 90° indicate?

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

  The final model of the atom
• What was discovered about the positive charge of the nucleus later on?

  It could be subdivided into smaller particles called protons
• Who provided evidence for the existence of neutrons?

  James Chadwick
• What is radioactive decay?

  A random process where unstable nuclei give out radiation to become more stable
• What is the unit of measurement for activity in radioactive decay?

  Becquerel (Bq)
• What is count-rate in the context of 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)
  • Neutrons: Not specified
• 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 half-life?

  The time taken for half the nuclei in a sample to decay