1. Nuclear Chemistry Nucleons vs. Nuclide  Nucleons: General name referring to nucleus made up off Protons + Neutrons  Nuclide: Nuclear chemistry’s way of referring to the atom For example: For example: Radium-228 orRadium-228 or

2. The Nucleus RRRRemember that the nucleus is comprised of two subatomic particles; protons and neutrons. TTTThe number of protons is the atomic number. TTTThe number of protons and neutrons together is effectively the mass of the atom.

3. The difference between the mass of an atom and the sum of the masses of its protons, neutrons, and electrons is called the mass defect. Mass Defect and Nuclear Stability The measured mass of, 4.002 602 amu, is: 0.030 377 amu less than the combined mass, 4.032 979 amu.

4. Mass Defect  Mass Defect: Difference between mass of atom and sum of masses of it’s p +, n, and e -  For example: Helium-4 Helium-4 2 Protons= (2 x 1.007276)2 Protons= (2 x 1.007276) 2 Neutrons= (2 x 1.008665)2 Neutrons= (2 x 1.008665) 2 Electrons= (2 x.0005486)2 Electrons= (2 x.0005486)______________________________4.032979 But its actual mass is measured at 4.00260 that’s.03038 less

5. Where did the.03038 go? It was converted to energy when formed Nuclear Binding Energy: energy released when nucleus is formed E = mc 2

6. Albert Einstein  Studied the mass and energy of atoms and found the relation between the two  Came up with the equation E = mc 2  Led to the understanding of binding energy (energy that holds an atom together)  Band of Stability: Most stable nuclei are 1:1 Most stable nuclei are 1:1 ( Proton: Neutrons) ( Proton: Neutrons)

7. Isotopes  Not all atoms of the same element have the same mass because of different numbers of neutrons in those atoms.  For example, there are three naturally occurring isotopes of uranium: Uranium-234 Uranium-234 Uranium-235 Uranium-235 Uranium-238 Uranium-238 All isotopes of uranium have 92 protons, but they all have different numbers of neutrons

8. Stability of Isotopes TTTThe “like” charges of the protons in the nucleus push the particles apart from each other, threatening to push the nucleus apart BBBBinding energy keeps the nucleus together SSSStable atoms have a binding energy that is strong enough to hold the nucleus together BBBBecause some isotopes have an extra neutron (or more), the binding energy cannot hold the nucleus together TTTThis makes the atom unstable These are radioisotopes

9. What is radioactivity? RRRRadioactivity is the act of emitting radiation spontaneously with the resulting emission of radiation resulting in the formation of a new nuclei Does not need a source to travel through space and penetrate another material AAAAtoms with unstable nuclei are radioactive Usually the number of neutrons will determine if a nuclei is unstable

10. Transmutation EEEElements with atomic numbers greater than 83 are radioisotopes Those elements with atomic numbers less than 83 have isotopes and most have at least 1 radioisotope RRRRadioisotopes try to stabilize They try to transform into a new, stable element This is transmutation The change occurs due to changes in the nucleus and results in radioactive decay

11. Radioisotope Half-Life  Radioisotopes are unstable. They decay, or change into new elements, over time.  The half-life of an element is the time it takes for half of the material you started with to decay. Remember, it doesn’t matter how much you start with. After 1 half-life, half of it will have decayed. Remember, it doesn’t matter how much you start with. After 1 half-life, half of it will have decayed.  Each element has its own half life.

12. Half-Life Questions  What is the half-life of this element? Half-life is where ½ of the element remains Half-life is where ½ of the element remains Go to 50% on the y-axis Go to 50% on the y-axis Then drop down to x-axis and that is the half-life Then drop down to x-axis and that is the half-life 1,000,000 years 1,000,000 years  What percent of the material originally present will remain after 2 million years? Go to 2 million on x-axis Go to 2 million on x-axis Go over to y-axis Go over to y-axis 25% 25%

13. Half-life calculations m f = m i (.5) n m f = m i (.5) n m f : final mass of sample m i : initial mass of sample n: number of half-lives t f = t 1/2  n t f = total time of decay t 1/2 = half life n = number of half-lives

14. Example problem:  Chromium-48 has half-life of 21.6 hours. How long will it take 360.0 g of Cr-48 to decay to 11.25 g? 108hours  If the half-life of tungsten-190 is 30.0 minutes, how much tungsten-90 will remain after 114 minutes if I’m originally given a 400.0 gram sample? 28.7 g

15. Types of Radioactive Decay SSSSpontaneous breakdown of a nucleus resulting in release of energy and matter TTTType of radiation emitted by radioactive materials RRRRadioactive decay and transmutation occur simultaneously CCCConstantly releasing energy and matter as they are transforming into a new, stable isotope Alpha Beta Gamma Positron

16. Alpha Decay α  Alpha decay results when an unstable nuclei loses a Helium-4 particle (2 protons and 2 neutrons) The new nucleus will have an atomic The new nucleus will have an atomic number that is 2 less than the original The new nucleus will have a mass The new nucleus will have a mass number that is 4 less than the original

17. Beta Decay β  Beta decay occurs when a neutron in an unstable nucleus splits to make a proton and a electron The atomic number increases by 1 because of the extra proton The atomic number increases by 1 because of the extra proton The mass number does not change since one neutron is subtracted, but one proton is added The mass number does not change since one neutron is subtracted, but one proton is added

18. Gamma Ray γ  Energy is emitted from the nucleus in the form of gamma rays Electromagnetic waves with very high frequencies and energy Electromagnetic waves with very high frequencies and energy Naturally occurring waves (identical to X-rays) Naturally occurring waves (identical to X-rays) Very dangerous to life Very dangerous to life Usually accompanies alpha or beta decay Usually accompanies alpha or beta decay

19. Positron Decay β + OOOOpposite of beta decay OOOOccurs in nuclei with too few neutrons PPPProton turns into a neutron AAAAtomic number decreases by 1 but mass number stays the same

20. Penetrating Ability

21. Nuclear Equations  Nuclear Equations show the original radioisotope and also tell you which type of decay that radioisotope underwent All you have to do is add or subtract to determine which type of decay occurred All you have to do is add or subtract to determine which type of decay occurred Example: Example: Loss of 2 protons Loss of 4 from the mass number That means it had to undergo alpha decay

22. Example problems a) Beta decay = extra proton X = 83 b) Alpha decay y = 206; x = 82 c) Increases by one proton x = electron d) Gamma radiation Y = 226; x = 88 e) Beta decay X = 214; y = 84 f) Alpha decay X = 226; y = 88 g) Alpha decay X = helium atom h) Gamma radiation x = same as on left