Atoms and radiation

• An atom has a small positively charged nucleus surrounded by orbiting electrons
• electrons are arranged at different energy levels
• most of an atoms mass is in its nucleus
• Protons:

  • relative mass is 1
  • Found in the nucleus
  • tells us the atomic number
• Electrons:

  • relative charge -1
  • same number of protons as electrons
  • orbits the nucleus
• Neutrons:

  • relative charge 0
  • found in the nucleus
• Ernest Rutherford discovered the nucleus by firing alpha particles at thin gold foil in 1909
• JJ Thomsons plum pudding model in 1897 discovered electrons
• In 1932 James Chadwick discovered neutrons
• Neil’s Bohr showed that electrons orbit
• Electrons are arranged in shells surrounding the nucleus
• When atoms absorb electromagnetic radiation the move to a higher energy level further from the nucleus
• When atoms emit electromagnetic radiation electrons move to a lower energy level closer to the nucleus
• The mass number is the protons + neutrons
• Atoms of the same element can have a different number of neutrons
• atoms have no overall electrical charge
• Atoms turn into positive ions when the lose electrons
• Atoms turn into negative ions when they gain electrons
• atoms of the same element with different neutrons are isotopes
• Hydrogen has three isotopes

  1. protium
  2. tritium
  3. deuterium
• Included are types of isotopes with specific nucleus that contain certain numbers of protons and neutrons