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The Nucleus

The Nucleus. The nucleus of an atom contains two types of particles. Proton. Neutron. These particles can be attracted to each other by the nuclear force. A chemical element is defined by the number of protons. Hydrogen. Helium. Lithium. But the charges pose a problem…. Helium.

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The Nucleus

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  1. The Nucleus

  2. The nucleus of an atom contains two types of particles Proton Neutron

  3. These particles can be attracted to each other by the nuclear force

  4. A chemical element is defined by the number of protons Hydrogen Helium Lithium

  5. But the charges pose a problem… Helium The positive charges of the protons prevent the nuclear force from keeping them together.

  6. But the charges pose a problem… Helium The neutral charge of the neutron allows more than one proton to be present.

  7. Isotopes are elements that have forms with different atomic masses. Lithium – 7 (%92.5 of all lithium) Lithium – 6 (%7.5 of all lithium)

  8. The average atomic mass (periodic table) is a weighted average of all the isotopes of that element Average = (7Li atomic mass x abundance) +(6Li atomic mass x abundance) Weighted average atomic mass Average = (7 x %92.5) +(6 x %7.5) 6.9 3 6.9 Li

  9. Some isotopes have too many or not enough neutrons and are unstable Carbon - 12 Carbon - 13 Carbon - 14

  10. Some isotopes have too many or not enough neutrons and are unstable Carbon - 14

  11. Some nuclei become so unstable that they release energy (radioactive)This happens in one of three ways… Alpha Decay – Nucleus releases 2p+and 2n0 Beta Decay – Nucleus releases 1e- and a n0becomes a p+ Gamma Decay – Nucleus releases a gamma ray (energy) Images from wikipedia

  12. Radioactive Decay 6 p+ 8 n0 14C Neutron Proton 7 p+ 7 n0 14N Electron

  13. Different types of radiation require different levels of protection Sheet of paper Sheet of aluminum Thick layer of lead Images from wikipedia

  14. Decay and Half-Life • Nuclei decay in a very predictable way. • Half-Life: The time it takes for one half of the sample to decay. • If you had 100 atoms of Carbon-14, it would take 5730 years for 50 of them to become Nitrogen-14. • If you had 1,000,000 atoms of C-14, it would take 5730 years for 500,000 of them to become N-14.

  15. Decay and Half-Life 25 atoms of 14C 50 atoms of 14C 100 atoms of 14C 12-13 atoms of 14C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C N N N N N N N N N N N N N N N N N N N N C C C N N N N N N N N N N N N N N N N N N N N N N C N N N N N N N N N N N N N N N N N N N N C C N N N N N N N N N N N N N N N N N N N N N N N N N 3(5730 years) = 17910 years 2(5730 years) = 11460 years 5730 years

  16. A fission reaction is where a very heavy nucleus (U, Pu) is split to release two small nuclei, neutrons, and a great deal of energy Ba-141 Kr-92 U-235 neutrons

  17. A chain reaction…

  18. Fusion reactions involve two smaller nuclei joining to become a bigger nucleus

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