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2. Atoms and Elements chapter 2

2. Atoms and Elements chapter 2 Scanning Tunneling Microscope (STM) Image of gold atoms (Nanotechnology) Atomic radius of gold is ~ .2 nm (1 nm =10 -9 m or one billionth of a metre). Subatomic Particles (to Chemists).

walter-hebert
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2. Atoms and Elements chapter 2

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  1. 2. Atoms and Elements chapter 2 Scanning Tunneling Microscope (STM) Image of gold atoms (Nanotechnology) Atomic radius of gold is ~ .2 nm (1 nm =10-9m or one billionth of a metre)

  2. Subatomic Particles (to Chemists) A proton is a sub- atomic particle with a mass of 1 amu and a charge of +1 A neutron is a sub- atomic particle with a mass of 1 amu and no electrical charge The nucleus is the positively charged central core of an atom An electron is a subatomic particle with negligible mass and a charge of -1

  3. Subatomic Particles Location in atom grams amu Charge Neutron Proton Electron 1.68 x 10-24 1.67 x 10-24 0.0009 x 10-24 1 1 0 Nucleus Nucleus Outside the nucleus 0 1+ 1- An atomic mass unit(amu) is exactly 1/12 the mass of the most common kind of carbon atom. This gives the proton a mass of 1.007(~1) amu, the neutron a mass of 1.009(~1) amu and the electron a mass of 0.0005(~0) amu.

  4. Element Distribution(by atoms) Universe 90% Hydrogen >9% Helium <0.3% all others Human Body 63% Hydrogen 25.5% Oxygen 9.5% Carbon 1.5% Nitrogen 0.5% all others

  5. Origin of the elements • Big bang created the lighter elements-ie H, He, Li Be and Boron (B) ~15 billion years ago • Theory suggests that it takes ~700 million years for H and He to coalesce into stars • Nuclear reactions inside stars are believed to produce the heavier elements • Infrared (IR) data from the Hubble telescope indicates the presence of heavy elements such as Iron and Zinc in stars

  6. Origin of the Earth • Formed ~ 5 billion years ago • Solidified cloud of dust and gases left over from creation of the Sun • Iron and silicates main ingredients, along with small amounts of other elements • Resulting heavy iron core produces magnetic field • Silicates are major part of Earth’s crust

  7. Water on the Earth • As Earth cooled, fairly stable “crust” formed • Depressions in the crust were natural basins in which water arising from volcanoes and fissures, collected to form oceans

  8. Origin of life on Earth • Water required • Anerobic conditions for first bacteria • Fossil remains give carbonaceous material on Earth aged 3.5 billion years ago • Details still not known! • Evolution vs Creation!!

  9. What’s in a Name? • Hydrogen: from Gr. hydro genes (water forming). Identified as an element by Henry Cavendish in 1766 • Helium: From Gr. Helios (sun); made by fusion in the sun-1st identified on Earth by William Ramsay in 1895

  10. In all atoms of all elements, the number of electrons surrounding the nucleus exactly equals the number of protons within the nucleus.All atoms of all elements are electrically neutral. The mass number of an atom(A) is the sum of the protons and the neutrons in its nucleus. Because the mass of an electron is negligible compared with the mass of both a proton and the neutron, virtually the entire mass (99.95%) of an atom lies in its nucleus.

  11. The atomic number (Z) is the total number of protons in the nucleus of an atom All atoms of the same element have the same atomic number. Thus, an element is a substance whose atoms all have the same atomic number

  12. Mass number (A) - Atomic number (Z) = the number of neutrons. 19 F # of neutrons: 19-9 =10 9

  13. Isotopes are atoms with the same atomic number (ie.same element) but with different mass numbers. Isotopes of a particular element all have the same number of protons (same atomic number) but carry different numbers of neutrons in their nuclei (therefore different mass numbers). Isotopes: Deuterium and Tritium Naturally occurring deuterium is extremely rare; only about 1 D atom for every 67,000 H atoms 1 2 3 H H H 1 1 1 Tritium Protium Deuterium

  14. Stable Isotopes of Carbon • 126C natural abundance 98.892%, atomic mass 12.00000 • 136C natural abundance 1.108%, atomic mass 13.00756 amu • Thus atomic weight C =(.98892x12.00000) +(.01108x13.00756) = 12.01 amu

  15. The radioactive isotope of C • 14C is radioactive with a half life of about 5700 years. It is very useful in dating archeological artefacts with ages up to about 10 x the half life of 14C • Living matter has a constant (low) 14C content, due to 14CO2 in photosynthesis • 14C has 6 electrons and 8 neutrons • Shroud of Turin (Christ’s burial cloth?) No, 14C dating indicated it was only about 500 years old. • Spring 2009: 14C dating results questioned –impure sample?

  16. Shroud of Turin

  17. Isotopes in Nuclear Medicine • Modern diagnostic techniques use isotopes with short half lives • Technetium 99Tc (t1/2= 6hours) is most common: results from decay of 99Mo • Crisis at Chalk River (AECL) in Nov-Dec 2007 • Repair schedule caused disruptions in supply

  18. Production of short lived isotopes • Need a nuclear reactor • Start with a stable isotope of Molybdenum • Neutron activation of 9842Mo • 9842Mo + 10n  9942Mo (half life 67 hours) • a balanced “nuclear” equation

  19. Decay of 9942Mo • Goes spontaneously to 99Tc (t1/2=6 hours) • Emits gamma rays (~ same E as X-rays) • Radiopharmaceuticals combine Tc with tin, pyrophosphate, monoclonal antibodies: for mapping circulatory disorders, heart muscle damage and intestinal cancers, respectively • Many other applications :over 30 radiopharmaceuticals presently in use

  20. Advantages of Tc imaging • Low doses of radioactivity used • Gamma radiation emitted is detected with an X-ray “camera” more sensitive than X-ray absorption • Short half life (6 hr) means that in 24 hours; 4 half lives ie.5x.5x.5x.5=.0625 Tc remains • Thus only 6% of the radiation still in the body after 1 day

  21. Isotopes in the House of Commons • Rumour has it that PM Harper called up Bush to discuss the “problem with the Isotopes” • “Fallout”: President of AECL resigned • Safety concerns were trumped by the need to get the supply up and running again

  22. A Continuing Problem • AECL reactor at Chalk River is 50 years old • Supplies ~half of all medical imaging isotopes used globally and almost all of those in NA. • Suppliers outside Canada now being sought • need Health Canada approval • Stayed tuned!!

  23. Iodine -131 in Ottawa waste • Biosolids showed low levels of radioactivity in Feb 2009,due to iodine 131. Commonly used medical isotope-particularly for thyroid disorders: levels deemed too low for concern • Half life~8days; beta and gamma emitter • 131MIBG (meta-iodobenzylguanidine) used for cancer treatment • Formed by fission of 235U; decays giving γ radiation, a beta particle (-1β0) and 54Xe131. Chernobyl (1986) accident-large amounts of 131-iodine given off- thyroid cancers in children observed

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