What is Nuclear Chemistry?

1. What is Nuclear Chemistry? Mr. McCord’s 10th Grade Chemistry Class Click Here to Jump In!

2. IntroductionWhat is Nuclear Chemistry? “Nuclear Chemistry is the study of nuclear reactions, with an emphasis on their uses in chemistry and their effects on biological systems” (Chemistry: The Central Science - 10th Edition, 2006). So, that’s great and all… but what does that really mean? Next Slide

3. IntroductionWhat is Nuclear Chemistry? In Chemistry, “Nuclear” refers to the atomic nucleus: the massive, positively-charged center of the atom built of protons and neutrons. Therefore, “nuclear reactions” are just changes concerned with the nuclei of atoms! Nuclear Chemistry is a seriously cool, ever-growing side of chemistry, explaining abstract and complex scientific phenomena! The existence and extreme brightness of stars comes from the incredible energy released from a nuclear reaction called fusion, where Hydrogen atoms collide and combine their nuclei to form Helium atoms! Next Slide

4. IntroductionWhat is Nuclear Chemistry? Nuclear Chemistry is a field that is expanding at an incredible rate, and by collaborating with our friends in Physics, we’ve made some amazing discoveries in the nitty-gritty, itty-bitty side of science! Proceed to learn about the fundamentals of Nuclear Chemistry, give it some thought, then take the quiz to prove your newfound knowledge! Go forth and discover! Next Slide

5. Main Menu Learn About It! Think About It! (Apply It!) Quiz! *Back to the Title *Back to the Introduction

6. Learn About It!Review on Reactions Go to the next slide and click on the video for a quick recap on reactions! This will also help you transition into the new material! Home To the Video!

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8. Learn About It!Crash Course on the Nucleus Key Vocabulary Nucleus: Center of the atom. Contains massive protons & neutrons. Protons and neutrons are essentially equal in mass. Protons: Determine the element. Positively charged. Neutrons: Determine the isotope. Isotopes: Atoms of the same element that have different numbers of neutrons (different mass numbers). Different isotopes of the same element often vary in stability, due to the number of neutrons in comparison to the number of protons (proton-neutron ratio) or due to the large number of both combined. Helium Nucleus mass # = # protons + # neutrons atomic # = # protons only (# = number) Prev. Slide Home Next Slide

9. Learn About It!Isotopes and Stability All elements have isotopes: atoms that have the same atomic number (number of protons) but a different mass number (total number of protons and neutrons). Some isotopes occur more commonly than others, and some are more stable than others as well! The stability, like all other nuclear properties, depends on the number of protons and neutrons. A fundamental phenomenon of nature called the strong force holds the protons and neutrons together in the nucleus, but when the nucleus becomes overcrowded, the strong force is not enough to keep the nucleus together and stable! The unstable nucleus must do something to return to a low-energy state! Prev. Slide Home Next Slide

10. Learn About It!The Unstable Nucleus & Radioactivity With too much stuff in the nucleus, instability strikes! An unstable nucleus is also called a radionuclide, and by extension, isotopes with radionuclides are called radioisotopes. Makes sense, right? “Radio” might sound familiar, like when you think of the radio you listen to in the car, but you also might recognize it from the word “radioactive.” Radioactivity is a general term used to describe instability that is relieved by some means. When an isotope is radioactive, it must do something to “relax,” in a sense. But atoms can’t settle down by sipping lemonade on a beach or reading a book by the firelight like we can. Instead, they must make a nuclear change to obtain a state of stability. This nuclear change is called radiation. Prev. Slide Home Next Slide

11. Learn About It!Types of Radioactivity Radiation is also referred to as radioactive decay. In the process of radioactive decay, the radioisotope throws stuff away from the nucleus. After all, the stuff in the nucleus is what’s causing the problem, right? There are three main types of radioactive decay: • Alpha Decay – An alpha particle () is emitted from the unstable nucleus. An alpha particle is essentially a helium nucleus (two neutrons, two protons) thrown from the radionuclide. • Beta Decay – A beta particle () is emitted from the unstable nucleus. A beta particle is essentially an electron () thrown from the radionuclide. • Gamma Decay – Gamma radiation () is emitted from the unstable nucleus. A gamma ray is essentially very high-energy light thrown from the radionuclide. Prev. Slide Home Next Slide

12. Learn About It!Alpha Decay When an isotope of an element has a very large mass number (a lot of protons and neutrons), a lot of energy is pent up excessively in the nucleus. To release this energy, an Alpha Particle may be released: An alpha particle is composed of 2 protons and 2 neutrons (a Helium nucleus). When -decay occurs, the isotope’s element changes, becoming the element two places before it on the periodic table. Some examples can be seen on the next slide!  Prev. Slide Home Next Slide

13. Learn About It!Examples of Alpha Decay Uranium-238 undergoes alpha decay, turning into Thorium-234 as the alpha particle is emitted Radium-222 undergoes alpha decay, turning into Radon-218 as the -particle (He nucleus) is emitted Polonium-208 undergoes alpha decay, turning into Lead-204 as the alpha particle is emitted Prev. Slide Home Next Slide

14. Learn About It!Beta Decay Early on in the periodic table, it is normal to see a stable isotope which has a proton-neutron ratio of about 1:1 (one proton for every neutron). However, as the number of protons in an atom gets very large down the periodic table, we see that isotopes are more stable when there are more neutrons than protons. Despite this, it is very possible for there to be too many neutrons, even considering the increased ratio. In this case, a neutron converts to a proton and an electron, where the proton stays bound in the nucleus, and the electron is emitted as a Beta Particle: The resulting proton changes the element and helps to balance the proton-neutron ratio. Thus, the Atomic Number increases by one, and the Mass Number stays the same. Prev. Slide Home Next Slide

15. Learn About It!Examples of Beta Decay Cobalt-60 undergoes beta decay, turning into Nickel-60 as the beta particle is emitted Copper-64 undergoes beta decay, turning into Zinc-64 as the -particle (high-energy electron) is emitted Cesium-137 undergoes beta decay, turning into Barium-137 as the beta particle is emitted Prev. Slide Home Next Slide

16. Learn About It!Gamma Decay Alpha and beta decay both restore stability in the nucleus of an isotope by altering the number of protons and neutrons, but after these two types of decay, the atom is often left in an excited, energetic, unstable state. To further stabilize, the nucleus emits energy in the form of high-energy Gamma Rays: A gamma ray is an electromagnetic wave of very high frequency – essentially, very high-energy invisible light.  Prev. Slide Home Next Slide

17. Learn About It!Examples of Gamma Decay As Polonium-215 undergoes alpha decay, the resulting Lead-211 is excited, and must stabilize by also emitting a gamma ray. Gamma radiation often accompanies other types of decay, as seen here. As Technetium-99 undergoes beta decay, the resulting Rutherfordium-99 is excited, and must stabilize by also emitting a gamma ray. Barium-137 is an excited isotope of Barium. A gamma ray is emitted to stabilize, and no change in mass number or element is made. Prev. Slide Home Next Slide

18. Learn About It!Alchemical Transmutations Through alpha and beta decay, we see the element of an atom can change with the loss or gain of protons! This change of element is often referred to as a transmutation. Alchemists attempted to achieve transmutation in order to change Lead (a typically common, low-worth metal) into gold (a very precious metal). Their attempts were unsuccessful, and they never achieved true transmutation, because they did not fully understand the difference between atomic and nuclear changes. All they did was change the arrangement of different elements in compounds and molecules. These combination and replacement reactions do not cause nuclear changes, as the electrons are the key particles in bonding (forming compounds and molecules). No change in protons would ever result from such reactions. Prev. Slide Home Next Slide

19. Learn About It!Radioactive Decay Series Before we move past the atomic scale, there is one more important note on radiation. In some cases, decay is not “one and done.” After one decay, the isotope may still be unstable or excited, so another decay is needed to stabilize the isotope. This was touched upon with gamma decay. Large, very unstable isotopes may take quite a few steps to stabilize, especially in larger-mass isotopes (Uranium-238 is a good example). This multi-step process of nuclear reactions ending with a stable isotope is called a Radioactive Decay Series. Prev. Slide Home Next Slide

20. Learn About It!Radiation on the Macroscopic Scale So, now we know the why’s and how’s about radiation on the atomic scale, but what about on our naked-eye, macroscopic scale? Can we measure it? Is it even important for anything? ? ? ? The answer is yes; radiation does not go unnoticed! Even though we can’t directly see it, we can definitely observe its effects. We can measure it for safety precautions, scientific discovery, and energy source research. One big difference from the theoretical material we’ve covered so far is that we hardly ever see just one or a few radioactive atoms when we study their effects – we’re more interested in tons and tons of radioactive atoms! But how will this change our view of decay for large samples and what we look for in nuclear reactions? Prev. Slide Home Next Slide

21. Learn About It!Half-Life of Isotopes One nifty rule that we have figured out about radioactive samples on a macroscopic scale is that it takes a specific amount of time for half of the sample’s radioactive atoms (of a certain isotope) to decay. This is called the isotope’s Half-Life. For instance, it takes about 5,730 years for half of a sample’s radioactive Carbon-14 atoms to decay, no matter the sample size. To this day, it is still unknown why this happens so certainly, but it definitely happens. We also can’t determine which atom will decay at what time! 0 yrs. No Half-Lives 100% C-14 5,730 yrs. 1 Half-Life 50% C-14 11,460 yrs. 2 Half-Lives 25% C-14 17,910 yrs. 3 Half-Lives 12.5% C-14 Prev. Slide Home Next Slide

22. Click on this video for a further explanation of Half-Life! Prev. Slide Home Next Slide

23. Learn About It!Energy of Radiation Another macroscopic property of radiation we can measure is how the energy of radioactive decay effects the distance the radiation can travel, as well as how far it can pass though given materials! For instance, we’ve found that an alpha particle only travels a short distance and doesn’t penetrate very far through materials when emitted. This is attributed to its high mass and slow speed in comparison to other types of decay, and thus, lower energy. Gamma rays, on the other hand, travel very fast over far distances, permeating far through many materials, due to their high-energy characteristic. Beta particles beat alphas in distance, speed, penetrating ability, and energy, but gamma rays take the cake! Prev. Slide Home Next Slide

24. Learn About It!Background Radiation There are two main reasons why the speed, distance, and penetration matter to us in the macroscopic world! 1st: Radiation is all around us in small, harmless doses. This naturally-occurring radiation is called background radiation. However, if we get careless, improper disposal of radioactive chemical waste can cause huge amounts of concentrated radioactivity, with doses hefty enough to do significant damage! 2nd:By evaluating the radiation around us, we can find out when we are at risk (higher energy, speed, etc. = more dangerous!). For instance, gamma rays can ionize tissue, easily damaging biological systems. The damages done by ionizing radiation can cause malfunctions in the processes of cells! Ouch! Now, proceed to the next slide to “Think About It!” Prev. Slide Home Think About It!

25. Think About It!Too Much Stuff! When the nucleus is packed with too many protons and neutrons, or when there are too many neutrons in comparison to the number of protons, the nucleus is unstable! One way to think of it is a person carrying too many books: With too many books, this guy can’t keep them balanced! He’ll have to lose a few books (undergo nuclear change) to regain his balance (return to a stable state)! Need to lose stuff! Goes through decay! Home Next Slide

26. Think About It!Can the Alchemist’s Dream come True? Back in the archaic times of chemistry, alchemists sought to turn Lead into Gold. Their methods only dealt with the bonding of elements, and thus, they never truly transmuted (changed from one element to another), but what about today? It is possible to force transmutations by firing high-energy neutrons through a particleaccelerator at a sample of lead, causing it to change elements, but since this method is very costly and complex, the extremely small amount of gold formed would not be nearly enough to turn a profit or compensate for the resources, as hoped by the alchemists. Prev. Slide Home Next Slide

27. Think About It!Losing a “Series” of Books If we think back to the guy holding tons of books, he would have to set some books down to keep his stack balanced. Most likely, setting just one book down isn’t going to cut it. Large isotopes have the same problem! They’ll often decay multiple times (in a series) in order to stabilize. For instance, Uranium-238 has a radioactive decay series of 14 steps to reach a stable form, Lead! Prev. Slide Home Next Slide

28. Think About It!Radiocarbon Dating When geologists take core samples of rock layers, they can look at the materials in each layer to give a relative age of the layers around it (called relative dating). However, radiocarbon dating takes advantage of our nuclear knowledge to find more accurate ages of really old things! Carbon-14 is found in organisms and many other things, so we can use Carbon-14’s constant decay rate to look at the remaining amount of radioactive isotope within the organic material, then use the half-life of Carbon-14 to calculate the time spent decaying! This has been used to date historical artifacts, such as the Dead Sea Scrolls, the Shroud of Turin, and even Ötzi the Iceman! (The Dead Sea Scrolls, dated around 408 BCE to 318 CE, are behind the title of this slide!) Prev. Slide Home Next Slide

29. Think About It!Popcorn Popping! If you were making a bag of popcorn, would you be willing to bet your friend five bucks that you could guess which kernel would pop first? I wouldn’t! There’s just waaaytoo many possibilities with no reasonable way of guessing! This is a great analogy for predicting the decay of atoms in a radioactive sample. So far, there’s just no mathematical or statistical way to determine which exact atom will undergo a nuclear change at some given time, and good guessing wouldn’t really help anyone! All we know is that the sample will lose half of its amount of radioisotope every half-life. Thankfully, as of yet, we don’t need to know which atom will decay at what time, nor the order of decay for the atoms. Until a brilliant nuclear chemist or nuclear physicist comes up with an application, the only thing we’d get from it anyway would be bragging rights (or maybe five bucks)! Who knows, that nuclear scientist could be you! Prev. Slide Home Next Slide

30. Think About It!Geiger Counters We discussed Background Radiation and the risks of high-dosage radiation, but how do we know where we are at risk? A Geiger Counter is an instrument that uses a low-pressure tube to sense, or “count,” interactions of ionizing radiation (, , and , for example). These “counts” are indicated by audible clicks, produced when the radiation interacts with the gas in the tube and briefly conducts an electrical charge. More clicks means more radiation, and more radiation means the area you’re inspecting is more dangerous! Prev. Slide Home Take the Quiz!

31. QUIZ! Think you have the concepts down? Test your knowledge and prove yourself! Show that you are a master of Nuclear Chemistry! Start the Quiz! Home

32. Question #1 Uranium-238 () is an isotope of Uranium that has almost 3 times as many neutrons as protons in its nucleus. It is very massive in comparison to isotopes found earlier on the periodic table. Would Uranium-238 be a radioactive isotope of Uranium? Yes No

33. Correct! Yes, Uranium-238 is a radioactive isotope! It will emit an -particle to become Thorium-234. Keep it up! Next Question!

34. Whoops, Try Again! If you need help, check this out to review before you try again! Back to Alpha Decay!

35. Learn About It!Alpha Decay When an isotope of an element has a very large mass number (a lot of protons and neutrons), a lot of energy is pent up excessively in the nucleus. To release this energy, an alpha particle may be released: An alpha particle is composed of 2 protons and 2 neutrons (a Helium nucleus). When -decay occurs, the isotope’s element changes, becoming the element two places before it on the periodic table. Some examples can be seen on the next slide!  Back to the Quiz!

36. Question #2 Name the three common types of radioactive decay discussed! a.) Alpha, Beta, Grammar b.) Omega, Mu, Gamma c.) Helium, Electron, Light d.) Alpha, Beta, Gamma

37. Correct! Right! The three most common types of decay for Nuclear Chemistry are Alpha (), Beta (), and Gamma () Decay! Good work! Next Question!

38. Whoops, Try Again! If you need help, check this out to review before you try again! Back to Types of Decay!

39. Learn About It!Types of Radioactivity Radiation is also referred to as radioactive decay. In the process of radioactive decay, the radioisotope throws stuff away from the nucleus. After all, the stuff in the nucleus is what’s causing the problem, right? There are three main types of radioactive decay: • Alpha Decay – An alpha particle () is emitted from the unstable nucleus. An alpha particle is essentially a helium nucleus (two neutrons, two protons) thrown from the radionuclide. • Beta Decay – A beta particle () is emitted from the unstable nucleus. A beta particle is essentially an electron () thrown from the radionuclide. • Gamma Decay – Gamma radiation () is emitted from the unstable nucleus. A gamma ray is essentially very high-energy light thrown from the radionuclide. Back to the Quiz!

40. Question #3 A nuclear change occurs in the nucleus of a radioisotope, and as a result, a high-energy electron is emitted. Name the type of decay that occurred! a.) Alpha () b.) Beta () c.) Gamma ()

41. Correct! The emission of a high-energy electron due to a nuclear change is characteristic of beta decay, where the high-energy electron is also called a beta particle! Way to go! Next Question!

42. Whoops, Try Again! If you need help, check this out to review before you try again! Back to Beta Decay!

43. Learn About It!Beta Decay Early on in the periodic table, it is normal to see a stable isotope which has a proton-neutron ratio of about 1:1 (one proton for every neutron). However, as the number of protons in an atom gets very large down the periodic table, we see that isotopes are more stable when there are more neutrons than protons. Despite this, it is very possible for there to be too many neutrons, even considering the increased ratio. In this case, a neutron converts to a proton and an electron, where the proton stays bound in the nucleus, and the electron is emitted as a Beta Particle: The resulting proton changes the element and helps to balance the proton-neutron ratio. Thus, the Atomic Number increases by one, and the Mass Number stays the same. Back to the Quiz!

44. Question #4 A radioisotope of Carbon known as Carbon-14 () has just undergone beta () decay, and it is still quite unstable. If the atom then undergoes gamma decay to stabilize, what is the final product? a.) b.) d.) c.)

45. Correct! Yeah! The beta decay is most important here for determining the final product, since gamma decay only releases energy from the nucleus without changing the makeup of the nucleus. Step 1: In Step 1, a neutron within the nucleus of Carbon-14 converts to a proton and an electron. The new proton sticks around in the nucleus, causing the element to change from Carbon to Nitrogen. The electron is thrown off at a high speed and energy as a beta particle. Step 2: In Step 2, the Nitrogen-14 is excited, and needs to release energy to stabilize. Thus, a gamma ray is emitted to allow Nitrogen-14 to become stable. Super! Next Question!

46. Whoops, Try Again! If you need help, check this out to review before you try again! Back to Examples of Beta Decay and Gamma Decay!

47. Learn About It!Examples of Beta Decay Cobalt-60 undergoes beta decay, turning into Nickel-60 as the beta particle is emitted Copper-64 undergoes beta decay, turning into Zinc-64 as the -particle (high-energy electron) is emitted Cesium-137 undergoes beta decay, turning into Barium-137 as the beta particle is emitted Next Slide

48. Learn About It!Gamma Decay Alpha and beta decay both restore stability in the nucleus of an isotope by altering the number of protons and neutrons, but after these two types of decay, the atom is often left in an excited, energetic, unstable state. To further stabilize, the nucleus emits energy in the form of high-energy Gamma Rays: A gamma ray is an electromagnetic wave of very high frequency – essentially, very high-energy invisible light.  Back to the Quiz!

49. Question #5 An ancient artifact is found containing a radioactive isotope throughout the sample! If the half-life of this isotope is 200 years, and 12.5% of the original amount of isotope remains, how old is the artifact? Hint: How many half-lives have passed? a.) 400 years old b.) 200 years old d.) 1000 years old c.) 600 years old

50. Correct! Indeed! When 12.5% of the original isotope remains, 3 half-lives have passed, and for each half-life, 200 years have passed. So, 3 half-lives multiplied by 200 years each equals 600 years passed! Excellent! 100% No Half-Lives 0 Years Passed 12.5% 3 Half-Lives 600 Years Passed 25% 2 Half-Lives 400 Years Passed 50% 1 Half-Life 200 Years Passed Next Question!