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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…. -_. -.

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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. Penetrating Powers of Radiation Penetrating Powers of Radiation

  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

  26. USES OF RADIOACTIVITY

  27. Radioactive tracer in medicine to find brain tumours

  28. Abnormalities with organs e.g. lungs

  29. Industrial Radioactive tracer: finding break in underground pipe RADIATION/FAULT IN PIPE DETECTED γ SOURCE USED AS RADIATION WILL NOT BE ABSORBED BY EARTH BREAK IN PIPE UNDERGROUND

  30. STERILIZATION OF SURGICAL EQUIPMENT AND FRESH FOOD

  31. CONTROL THICKNESS OF PAPER (β SOURCE) Radiation detector control 200 COUNTS/SECOND 150 COUNTS/SECOND 250 COUNTS/SECOND CORRECT THICKNESS PAPER TO THICK PAPER TOO THICK PAPER TO THIN Radiation source β Rollers to control thickness of paper

  32. CONTROL THICKNESS OF ALUMINIUM/STEEL (γ SOURCE) Radiation detector control 200 COUNTS/SECOND 150 COUNTS/SECOND 250 COUNTS/SECOND CORRECT THICKNESS PAPER TO THICK TOO THICK TO THIN Radiation source γ Rollers to control thickness of paper

  33. CARBON DATING OF ONCE LIVING THINGS ETC. FOSSILS

  34. DEAD – ORGANISM STOPS TAKING IN CARBON 14 AND RADIATION LEVEL BEGINS TO FALL ALIVE – RADIATION LEVEL CONSTANT HALF LIFE CURVE FOR CARBON 14 RADIATION LEVEL AGE OF DEAD ORGANISM

  35. EXAMPLES OF CARBON DATING TO FIND THE AGE OF :- • ROMAN SHIP • TURIN SHROUD

  36. Find radiation level of sample wood taken from ship BUILT 180 A.D. Find radiation level from wood from local tree Take piece of wood from local tree

  37. HALF LIFE GRAPH FOR CARBON 14 (finding age of ship) RADIATION LEVEL OF WOOD FROM TREE RADIATION LEVEL RADIATION LEVEL FROM WOOD FROM BOAT TIME (YEARS) AGE OF BOAT 1824 YEARS OLD

  38. Turin shroud Cotton plant

  39. HALF LIFE GRAPH FOR CARBON 14 (finding age of Turin Shroud) RADIATION LEVEL OF COTTON PLANT RADIATION LEVEL RADIATION LEVEL FROM CLOTH OF TURIN SHROUD TIME (YEARS) AGE OF SHROUD 1400 YEARS OLD

  40. Finding the age of rocks Uranium Lead Approximately 4500 000 000 years

  41. Rock Uranium Lead

  42. 1 half life later… 1 half life later… 1 half life later… 2 1 8 4 8 8 8 8 Question: Uranium decays into lead. The half life of uranium is approximately 4,500,000,000 years. A sample of radioactive rock contains 7 times as much lead as it does uranium. Calculate the age of the sample. Answer: The sample was originally completely uranium… …of the sample was uranium Now only 4/8 of the uranium remains – the other 4/8 is lead Now only 2/8 of uranium remains – the other 6/8 is lead Now only 1/8 of uranium remains – the other 7/8 is lead So it must have taken 3 half lives for the sample to decay until only 1/8 remained (which means that there is 7 times as much lead). Each half life is 4,500,000,000 years so the sample is 13,500,000,000 years old.

  43. Ionisation Powers of Radiation Prolonged exposure to ionising radiation is dangerous to humans. Ionisation is the ability of radiation to remove electrons from atoms which will then change their structure

  44. IONONIZATION ATOM WITH ELECTRONS DISPLACED ATOM

  45. Dangers of radioactivity – OUTSIDE BODY Alpha Radiation will ionise atoms in living cells – this can damage them and cause cancer or leukaemia. Beta Gamma Gamma OUTSIDE the body and  are more dangerous as they can penetrate the skin into your body to your organs.

  46. Dangers of radioactivity – INSIDE BODY Dangers of radioactivity (INSIDE BODY) INSIDE the body an  radiation is the most dangerous because it has not enough energy to pass out of the body and has the greatest ionization power to damage cells. β and γ are less dangerous because they have enough energy to pass out of the body Alpha Beta Gamma

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