atomic structure

• What model replaced the plum pudding model?

  Nuclear model
• What does the equality of protons and electrons in an atom imply?

  Atoms typically have no overall charge
• What happens to electrons when they gain energy?

  They move to a higher energy level
• What occurs when electrons release electromagnetic radiation?

  They move to a lower energy level
• What happens if one or more electrons leave an atom?

  The atom becomes a positively charged ion
• What do atoms of the same element have in common?

  Same number of protons
• What is the atomic number of an atom?

  Number of protons in an atom
• How is the mass number of an atom calculated?

  Protons + neutrons in the nucleus
• What are isotopes?

  Atoms with the same protons, different neutrons
• Do all elements have isotopes?

  Yes, but usually only one or two are stable
• What happens to unstable isotopes?

  They decay into other elements and emit radiation
• What is ionising radiation?

  Radiation that knocks electrons off atoms
• What is alpha radiation?

  Emission of an alpha particle from the nucleus
• What is an alpha particle composed of?

  Two neutrons and two protons
• How far can alpha particles penetrate materials?

  They are stopped quickly, absorbed by paper
• Why are alpha particles strongly ionising?

  Due to their size
• What are beta particles?

  Fast-moving electrons released by the nucleus
• How do beta particles affect the nucleus?

  A neutron turns into a proton during emission
• What materials can beta particles be absorbed by?

  Aluminium
• What are gamma rays?

  Waves of electromagnetic radiation from the nucleus
• How do gamma rays interact with materials?

  They penetrate far into materials
• What is the ionising power of gamma rays?

  Weak ionising power
• How are gamma rays absorbed?

  By thick sheets of lead or concrete
• What must be equal on both sides of a nuclear equation?

  Mass and atomic numbers
• What do nuclear equations show?

  Radioactive decay and emitted radiation
• What happens to the nucleus during alpha decay?

  Charge and mass of the nucleus decrease
• How does alpha decay affect protons and neutrons?

  It loses two protons and two neutrons
• How is an alpha particle represented?

  As $^{4}_{2}He$
• What occurs during beta decay?

  A neutron turns into a proton and an electron is released
• How does beta decay affect the charge of the nucleus?

  It increases the positive charge
• How is a beta particle represented?

  As $^{0}_{-1}e$
• What do gamma rays do to the nucleus?

  No change in charge or mass occurs
• What is the purpose of gamma rays?

  To get rid of excess energy from the nucleus
• How is gamma radiation represented?

  As $^{0}_{0}\gamma$
• What is radioactivity?

  A random process of radiation emission
• How is radiation measured?

  Using count rates
• What is a half-life?

  Time taken for radiation to halve
• How can half-life be used?

  To measure the rate of decay
• In what units is half-life measured?

  Becquerels (Bq)
• What happens to the radioactivity of a source over time?

  It decreases as stable nuclei form