1 Structure of a Nucleus Up to element 20- equal protons to neutrons After 20- more neutrons are necessary to keep the nucleus together Above 83- added neutrons cannot make nucleus stable

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3 Nuclear Chemistry

4 Radioactivity One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie ( ).One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie ( ). She discovered radioactivity, the spontaneous disintegration of some elements into smaller pieces.She discovered radioactivity, the spontaneous disintegration of some elements into smaller pieces.

5 Marie Curie Discovered Polonium and Radium Developed mini portable x-ray machine for use during WWI Died of aplastic anemia due to prolonged exposure of radiation Won Nobel Prize in Physics – 1903 Won Nobel Prize in Chemistry

6 Nuclear Reactions vs. Normal Chemical Changes “Normal” Chemical Reactions involve ELECTRONS, not protons and neutrons“Normal” Chemical Reactions involve ELECTRONS, not protons and neutrons Nuclear reactions involve the NUCLEUSNuclear reactions involve the NUCLEUS The breaking apart of the nucleus releases a tremendous amount of energy!The breaking apart of the nucleus releases a tremendous amount of energy!

7 Nuclear Reactions A reaction that changes the nucleus of an atom –Unstable nuclei –Changes the number of protons and neutrons –Gives off large amounts of energy –Increases stability in the process

8 Henri Becquerel Realized that photographic plates were being exposed to “rays” that were not caused by the sun since the plates were in a drawer. He had placed Uranium on a counter over the drawer! “Rays” were caused by radioactive decay

9 Radioactive Decay The spontaneous disintegration of a nucleus into a lighter nucleus with the emission of particles or electromagnetic radiation (or both)

10 Types of Radiation Alpha (ά) – a positively charged helium isotope Alpha (ά) – a positively charged helium isotope Beta (β) – an electronBeta (β) – an electron Gamma (γ) – pure energy; called a ray rather than a particleGamma (γ) – pure energy; called a ray rather than a particle

11 Neutron Neutron Positron – a positive electron Positron – a positive electron Proton – usually referred to as hydrogen-1Proton – usually referred to as hydrogen-1 Any other elemental isotopeAny other elemental isotope Other Nuclear Particles

12 Penetrating Ability Can also be blocked by clothing Can also be blocked by foil and water Can also be blocked by concrete

13 Alpha Decay (Emission) Loss of an  -particle (a helium nucleus) He 4242 U  Th He Types of Radioactive Decay

14 Alpha Radiation Limited to VERY large atoms.

15 Loss of a  -particle (a high energy electron) *Neutron changes into a proton (which stays in nucleus) and a beta particle is released (electron ejected from nucleus).  0 −1 e 0 −1 or I Xe  + e 0 −1 Beta Decay (Emission) Types of Radioactive Decay

16 Loss of a positron (a particle that has the same mass as but opposite charge than an electron) C 11 6  B e 0 +1 Positron Emission Types of Radioactive Decay Positron emission converts a proton to a neutron e 0 +1

17 Gamma rays are high energy photons produced in association with other forms of decay. Gamma rays are massless and do not, by themselves, change the nucleus Gamma Ray Production Types of Radioactive Decay

18 Complete the Nuclear Reaction Wkst as homework

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20 Stable Nuclei There are NO stable nuclei with an atomic number greater than 83. These nuclei tend to decay by alpha or beta emission.

21 Radioactive Decay Series An unstable radioactive nucleus reaches a stable state by a series of steps Graphic – Wikimedia Commons User Tosaka

22 Radioactive Decay Series Large radioactive nuclei cannot stabilize by undergoing only one nuclear transformation. They undergo a series of decays until they form a stable nuclide (often a nuclide of lead).

23 Complete the Decay Series Activity

24 Remember… Reactions can be –Chemical reactions where electrons interact –Nuclear reactions where nucleus breaks apart AND NOW…We can force these reactions to occur!!!!!

25 Artificial Nuclear Reactions New elements or new isotopes of known elements are produced by artificially bombarding (hitting) an atom with a subatomic particle such as a proton or neutron -- or even a much heavier particle such as 4 He or 11 B.

26 Artificial Nuclear Reactions Example of a  reaction is production of radioactive 31 P for use in studies of Phosphorous uptake in the body P n P +  

27 Aerial view of CERN and the surrounding region of Switzerland and France. Three rings are visible, the smaller shows the underground position of the Proton Synchrotron, the middle ring is the Super Proton Synchrotron (SPS) with a circumference of 7 km and the largest ring (27 km) is that of the former Large Electron and Positron collider (LEP) accelerator with part of Lake Geneva in the background.

28 September 10, 2008 The first beam in the Large Hadron Collider was successfully steered around the full 27 kilometres of the world's most powerful particle accelerator in Geneva, Switzerland.

29 Learning Check What radioactive isotope is produced in the following bombardment of boron? 10 B + 4 He ? + 1 n 5 2 0