4. Atomic Structure

• Atom


  The smallest part of an element that can exist, composed of protons, neutrons, and electrons
• Structure of an atom


  • Nucleus containing protons and neutrons
  • Electrons orbiting the nucleus at different energy levels
• Atomic number


  Indicates the number of protons in an atom's nucleus
• Mass number


  The total count of protons and neutrons in an atom
• Isotopes


  Different forms of the same element with the same number of protons but different numbers of neutrons
• The number of neutrons in an atom does not affect the charge of the atom, only its mass
• Development of the model of the atom


  1. John Dalton's solid sphere model

  2. J.J. Thomson's plum pudding model

  3. Ernest Rutherford's alpha particle scattering experiment
• The number of neutrons in an atom does NOT affect the charge of the atom, only its mass. This is because neutrons have no charge but do have mass.
• Atom


  A fundamental unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons
• Development of the Model of the Atom


  1. John Dalton proposed atoms were solid spheres, different spheres represented different elements

  2. JJ Thomson discovered electrons, leading to the "plum pudding model" of the atom

  3. Rutherford and Marsden's alpha particle scattering experiment disproved the plum pudding model, leading to the conclusion the atom consists mostly of empty space with a dense nucleus surrounded by electrons

  4. Niels Bohr refined the nuclear model by introducing the idea of electrons orbiting the nucleus in fixed shells

  5. James Chadwick discovered neutrons, solidifying the nuclear model
• Atoms and Nuclear Radiation
• Radioactive decay


  A process where unstable atomic nuclei release radiation to become more stable
• Activity


  The rate at which a radioactive substance decays, measured in Becquerels (Bq)
• Count-rate


  The number of decays detected per second, measured with a Geiger-Muller tube
• Alpha particles


  • Made up of two neutrons and two protons, have low penetration ability, strongly ionising
• Beta particles


  • High-speed electrons ejected from a nucleus, moderately ionising, have greater penetrating power than alpha particles
• Gamma rays


  • Electromagnetic radiation with no mass and no charge, have the lowest ionising power but can travel the longest distances
• Uses of Radiation


  • Alpha radiation in smoke detectors
  • Beta particles in material thickness measurement
  • Gamma rays as medical tracers
• Nuclear Equations


  1. Represent radioactive decay using element symbols

  2. Alpha decay decreases mass and atomic number

  3. Beta decay increases atomic number

  4. Gamma decay does not change mass or atomic number
• Half life


  The time it takes for the activity or number of undecayed nuclei to decrease to half of the original value
• Radioactive decay is a random process
• Radioactive contamination


  Radioactive particles come into direct contact with materials or living tissue, making the object radioactive
• Radioactive irradiation


  An object or person is exposed to radiation, but does not become radioactive
• The hazard from contamination and irradiation is influenced by the type of radiation emitted
• Scientific research on the effects of radiation must be published and peer reviewed to ensure accuracy and reliability