P4 - atomic structure

P4 - atomic structure

1. nucleus controls functions in cells, contains most of the mass

   • atom is smallest part

2. history of the atom

   • discovery and development of atomic theory
     • democitus - indivisible atomos
       • john dalton - atom was the building block of all things
         • jj thompson - plum pudding model, ball of positive charge dotted with negative charge
           • ernest rutherford - tiny nucleus has all mass and positive charge
             • niels bohr - electrons are in shells
               • james chadwick - discovered neutrons

3. p.e.n

   • proton / symbol - p / mass - 1 / charge - +ve / location - nucleus
     • neutron / symbol - n / mass - 1 / no charge or neutral / location - nucleus
       • electron / symbol - e / mass - tiny or 1/1836 / charge - -ve / location - shell

4. test questions

   • a smoke detector would not work if a radioactive source that emitted only gamma rays because gamma rays are not ionising enough and too penetrating
   • beta should be used to check welds in cracks because alpha cannot penetrate it and gamma would go straight through it
     • radioactive decay is random and spontaneous
   • irradiation - describes an exposure to radiation / someone who has been exposed to a radioactive source which isn’t on them or inside them
     • contamination - describes someone who has unwanted radioactive atoms on or inside them / the presence of unwanted radioactive atoms on or inside an object
   • nuclear fission is the splitting of an atomic nucleus / describes a uranium atom absorbing a neutron, then splitting into two smaller more stable atoms and emitting 2-3 neutrons
     • nuclear fusion is a nuclear reaction in which atomic nuclei of low atomic number fuse to form a heavier nucleus with the release of energy

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