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Nuclear model of atom

Nuclear model of atom. electron. -. proton. neutron. ELECTRON. Slide 19. PLUM PUDDING MODEL OF ATOM. A hundred years ago people thought that the atom looked like a “plum pudding” – a sphere of positive charge with negatively charged electrons spread through it…. -_. -.

zachery-guthrie
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Nuclear model of atom

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  1. Nuclear model of atom electron - proton neutron

  2. ELECTRON Slide 19

  3. PLUM PUDDING MODEL OF ATOM A hundred years ago people thought that the atom looked like a “plum pudding” – a sphere of positive charge with negatively charged electrons spread through it… -_ - Ernest Rutherford, British scientist: I did an experiment that proved this idea was wrong. I called it the “Rutherford Alpha particle scattering experiment”

  4. The Rutherford Scattering Experiment ALPHA PARTICLES GOLD LEAF ATOMS ++ - ++ ++ ++

  5. Differences between Thompson’s PLUM PUDDING model and NUCLEAR model of atom Plum pudding model Nuclear model Nucleus positively charged Most mass inside nucleus Mostly empty space Electrons orbit around nucleus Positively charged with electrons spread out inside

  6. ELEMENT SYMBOLS • An atom is represented by a symbol which will tell you:- • What element it belongs to. • Mass number (total number of protons + neutrons inside nucleus). • Atomic or Proton number (number of protons inside nucleus).

  7. Nucleus of Lithium atom 7 (Mass number) Li 3 protons 4 neutrons 3 (Atomic or Proton Number) Since all the atoms are neutral:- number of electrons orbiting around the nucleus = the number of protons inside nucleus so the number of electrons in this atom is 3.

  8. Nucleus of Magnesium atom 24 Mg 12 protons 12 neutrons 12 No of electrons = 12

  9. Nucleus of Aluminium atom 27 Al 13 protons 14 neutrons 13 No of electrons = 13

  10. There are 3 types of radiation α(alpha particle) Helium nuclei 2 protons and 2 neutrons β(beta particle) fast moving electron γ(gamma rays) electro magnetic waves All 3 types come from the nucleus of the atom!!

  11. Radioactive substances have atoms with unstable nuclei This means that there are an unequal number of protons and neutrons inside the nucleus

  12. NUCLEUS OF UNSTABLE ATOM Radiation is emitted when an unstable nucleus breaks down or disintegrates 2 PROTONS 2 NEUTRONS α β γ ELECTRO MAGNETIC WAVES FAST MOVING ELECTRON

  13. Radiation Symbol of alpha particle 4 4 He orα 2 2

  14. Radiation Symbol of beta particle 0 0 e orβ -1 -1

  15. Radiation Symbol of gamma ray γ

  16. NUCLEAR EQUATIONS Nuclear equations have to balance, just like chemical equations!!!!!!!!!!!!!!

  17. Alpha Emission: nucleus emits 2 protons and 2 neutrons X He Y 8 P 6p 9n 2p 2n + 11 N 4 19 15 X Y He + 8 6 2 Element X turns into element Y and emits an alpha particle

  18. Beta Emission: neutron turns into proton and electron. The electron is emitted from nucleus but the proton stays behind X β Y 3 P 5 N 4N 4p 4n 1e + 1P 1e 0 8 8 X Y β + 3 4 -1

  19. Gamma Emission: often occurs after alpha and beta emission. There is no change in mass or atomic number. Na e Mg 11 P 13 N 12 N 12P 12N 1e + 1P 1e 0 24 24 Na γ Mg e + + 11 12 -1 Example shows beta decay with gamma emission

  20. Nucleus • Contains protons and neutrons • Small Size • Relatively large mass • Extremely large density • Large amount of stored energy • Orbiting Electrons • Large size • Low density • Orbit nucleus near speed of light • Small amount of energy relative to nucleus • Responsible for chemical bonds

  21. Penetrating Powers of Radiation    Few cm of lead Sheet of paper Few mm of aluminium  particles cannot pass through paper  particles cannot pass through aluminium  particles cannot pass through lead

  22. HALF LIFE TIME TAKEN FOR ½ THE RADIOACTIVE ATOMS TO DISINTEGRATE OR TIME IT TAKES FOR THE RADIATION TO FALL TO ½ ITS ORIGINAL LEVEL

  23. Example of half life using pan of popcorn ‘popping’ 16 12 8 4 0 HALF LIFE OF POPCORN = 10s Number of popcorn remaining 0 10 20 30 40 50 Time (s)

  24. Question on half life of pop corn 32 24 16 8 0 The half life of popcorn is 20s. A sample contains 32 popcorn at the start. How many will be remaining after 60s? HALF LIFE OF POPCORN = 20s Number of popcorn remaining 4 0 20 40 60 80 100 Time (s) 4 32 16 8 4 ANSWER = 4 20s 20s 20s

  25. The half life of Americium is 433 years. A sample contains 480 nuclei. 1. How many will be remaining after approximately 1300years? 2. How long will it take to become harmless? Question on half life 480 360 240 120 0 Number of nuclei remaining 1. 60 nuclei • 6 x 433 years • = 2598 years 0 433 433 433 433 433 Time (years) 480 240 120 60 30 16 8 433 433 433 433 433 433

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