Atomic structure and radioactivity

• Describe the first atomic model.

  Small, solid, uncuttable spheres
• Describe plum pudding model.

  Cloud of positive charge containing negative electrons embedded in it
• Describe the nuclear model.

  A solid, positive, central nucleus with electrons orbiting around it
• Who discovered electrons?

  JJ.Thomson
• Who devised nuclear model?

  Rutherford
• Who discovered neutrons?

  Chadwick
• Who suggested existence on electron shells?

  Bohr
• Radius of an atom is 1×10‐¹⁰ m
• Radius of nucleus is 1×10‐¹⁴ m
• Proton

  mass = 1

  Charge =+1
• Neutron

  Mass = 1

  Charge = 0 neutral
• Electron

  Mass = very small

  Charge = -1 negative
• What does atomic number show?

  No. of protons in an atom
• What does atomic number show?

  No. of protons + No. of neutrons in an atom
• What happens to electrons when they absorb electromagnetic radiation?

  They move to a higher energy level further from the nucleus
• Isotope - atom with same No. of protons but different No. of neutrons
• Ion- a charged atom whkch has lost or gained electrons
• Radioactive decay - when an unstable atomic nucle randomly gives out radiation to become more stable
• Activity- rate of radioactive decay
• Activity is measured in becquerels (Bq)
• Types of radiation

  . Alpha

  . Beta

  Gamma
• Alpha is the most ionising
• Gamma is least ionising
• Alpha is least penetrating
• Gamma is most penetrating
• Half life


  Time taken for half the radioactive nuclei to decay
• Ionising


  Able to remove electrons from atoms
• Sieverts


  Unit of radiation dosage measured
• Short half life

  Hazardous because of high rate of decay
• Isotopes

  • Emit radiation
  • Unstable
• Nuclear fusion


  1. 2 small nuclei bond and release more energy

  2. Make a larger nucleus
• Nuclear fission


  1. Neutron fired at unstable nuclei

  2. Splits into 2 nuclei

  3. Releases 3 neutrons