1. The Nucleus

2. The nucleus of an atom contains two types of particles ProtonNeutron

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

4. A chemical element is defined by the number of protons HydrogenHeliumLithium

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 = ( 7 Li atomic mass x abundance) +( 6 Li atomic mass x abundance) Weighted average atomic mass Average = (7 x %92.5) +(6 x %7.5) 6.9 Li 36.9

9. Some isotopes have too many or not enough neutrons and are unstable Carbon - 12Carbon - 13Carbon - 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 2n 0 Beta Decay –Nucleus releases 1e - and a n 0 becomes a p + Gamma Decay – Nucleus releases a gamma ray (energy) Images from wikipedia

12. Radioactive Decay 6 p + 8 n 0 14 C NeutronProton Electron 14 N 7 p + 7 n 0

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

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 CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC 100 atoms of 14 C NNNNN NNNNNN NNNN NNNNN NNNN NNNNN NNNNN NNNNNN NNNNN NNNNN 5730 years 50 atoms of 14 C NN N NNN NNNN NNN NNNN NN NN NN NN 25 atoms of 14 C 2(5730 years) = 11460 years 12-13 atoms of 14 C NN NN N N NN N N NN 3(5730 years) = 17910 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 Kr-92Ba-141U-235 neutrons

17. A chain reaction…

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