NUCLEAR CHEMISTRY

STABILITY OF A NUCLEUS Nuclei are composed of protons and neutrons. Hydrogen is the exception. WHY?! Nuclear Stability – the larger (more massive) a nucleus is, the harder it is for it to stay together.

STABILITY OF A NUCLEUS Most nuclei are stable; “Belt of Stability” –Ratio of n 0 :p + in a stable atom varies with size –Small atoms are stable at a 1:1 ratio –As atoms become larger, more n 0 are needed for stability. Ratio of n 0 :p + can be driven as high as 1.5:1 Creates a zone of stability, inside of which the isotopes are stable. –Ex. C-12 C-14 Outside the zone, nuclei either have too many or too few neutrons to be stable.

Unstable nuclei therefore decay by emitting: α particles β particles γ particles to bring the ratio back to the zone of stability. All isotopes of all elements above Bi are unstable and undergo radioactive decay.

STABILITY OF A NUCLEUS When a nucleus is RADIOACTIVE, it gives off decay particles and changes from one element to another. This is also known as NATURAL DECAY or NATURAL TRANSMUTATION. Atoms with an atomic number of 1 – 83 have at least one stable (nonradioactive) isotope, but ALL isotopes of elements with an atomic number of 84 or more ARE radioactive.

How do nuclear reactions differ from chemical reactions? Chemical RxNuclear Rx Atoms of elements gain stability by losing or gaining e- Effected by changes in temperature, pressure, or the presence of a catalyst Requires energy Can be sped up, slowed down, or turned off. Nuclei of unstable isotopes gain stability by releasing decay particles that give off large amounts of energy. NOT effected by changes in temperature, pressure, or the presence of a catalyst. SPONTANEOUS – does not require energy. Cannot be sped up, slowed down, or turned off.

Answer Practice Problems #1-2 in Topic 12: Nuclear Chemistry note packet

STABILITY OF A NUCLEUS An unstable nucleus releases energy by emitting radiation during the process of radioactive decay. Types of Radioactive Decay Particles ParticleMassChargeSymbol Penetrating Power Alpha4 amu (made of 2 p + and 2 n 0 ) +2Low Beta0 amu (made of an e - ) Moderate Positron0 amu (made of an anti e - ) +1Moderate Gamma0 amuNone γ High

ALPHA RADIATION U Uranium-238 Th Thorium-234 He (  emission) 4242 Alpha particle Radioactive decay

ALPHA RADIATION When an atom loses an alpha particle, the atomic number of the product is lowered by two and its mass number is lowered by four. In a balanced nuclear equation, the sum of the mass numbers (superscripts) on the right must equal the sum on the left. The same is true for the atomic numbers (subscripts). U Th He 4242 →

Answer Practice Problems #15-16 in Topic 12: Nuclear Chemistry note packet

BETA RADIATION An electron resulting from the breaking apart of a neutron in an atom is called a beta particle. The neutron breaks apart into a proton, which remains in the nucleus, and a fast-moving electron, which is released. n 1010 Neutron p Proton e 0 –1 Electron (beta particle) → The –1 represents the charge on the electron. The 0 represents the extremely small mass of the electron compared to the mass of a proton. -

BETA RADIATION Carbon-14 emits a beta particle as it decays and forms nitrogen-14. The nitrogen-14 atom has the same mass number as carbon-14, but its atomic number has increased by 1. It contains an additional proton and one fewer neutron. C 14 6 Carbon-14 (radioactive) N Nitrogen-14 (stable) e (  emission) 0 –1 Beta particle →

BETA RADIATION A beta particle has less charge than an alpha particle and much less mass than an alpha particle. Thus, beta particles are more penetrating than alpha particles. –Beta particles can pass through paper but are stopped by aluminum foil or thin pieces of wood.

Answer Practice Problems #17-18 in Topic 12: Nuclear Chemistry note packet

POSITRON +

Answer Practice Problems #19-20 in Topic 12: Nuclear Chemistry note packet

TYPES OF RADIATION Because of their opposite charges, alpha and beta radiation can be separated by an electric field. Alpha particles move toward the negative plate. Beta particles move toward the positive plate. Gamma rays are not deflected.

GAMMA RADIATION A high-energy photon emitted by a radioisotope is called a gamma ray. The high-energy photons are a form of electromagnetic radiation. Nuclei often emit gamma rays along with alpha or beta particles during radioactive decay. Ra Radium-226 Th Thorium-230 He +  4242 Alpha particle Gamma ray → Pa Protactinium -234 Th Thorium-234 e +  0 –1 Beta particle Gamma ray →

GAMMA RADIATION Gamma rays have no mass and no electrical charge. Emission of gamma radiation does not alter the atomic number or mass number of an atom.

Gamma rays can be dangerous because of their penetrating power. What property determines the relative penetrating power of electromagnetic radiation?

REMEMBER High penetrating power

Gamma rays can be dangerous because of their penetrating power. What property determines the relative penetrating power of electromagnetic radiation? The wavelength and energy of electromagnetic radiation determine its relative penetrating power. Gamma rays have a shorter wavelength and higher energy than X-rays or visible light.

Answer Practice Problems #3-14 in Topic 12: Nuclear Chemistry note packet

NUCLEAR TRANSFORMATIONS The ratio between neutrons and protons. The nuclear force is an attractive force that acts between all nuclear particles that are extremely close together, such as protons and neutrons in a nucleus. At these short distances, the nuclear force dominates over electromagnetic repulsions and holds the nucleus together. What determines the type of decay a radioisotope undergoes?

NUCLEAR STABILITY AND DECAY Some nuclei are unstable because they have too many neutrons relative to the number of protons. When one of these nuclei decays, a neutron emits a beta particle (fast-moving electron) from the nucleus. –A neutron that emits an electron becomes a proton. –This process is known as beta emission. –It increases the number of protons while decreasing the number of neutrons.

NUCLEAR STABILITY AND DECAY Radioisotopes that undergo beta emission include the following.

NUCLEAR STABILITY AND DECAY Other nuclei are unstable because they have too few neutrons relative to the number of protons. These nuclei increase their stability by converting a proton to a neutron. –An electron is captured by the nucleus during this process, which is called electron capture.

NUCLEAR STABILITY AND DECAY Nuclei that have an atomic number greater than 83 are radioactive. These nuclei have both too many neutrons and too many protons to be stable. –Therefore, they undergo radioactive decay. –Alpha emission increases the neutron-to-proton ratio, which tends to increase the stability of the nucleus. Most of them emit alpha particles.

NUCLEAR STABILITY AND DECAY In alpha emission, the mass number decreases by four and the atomic number decreases by two.

NUCLEAR STABILITY AND DECAY Recall that conservation of mass is an important property of chemical reactions. In contrast, mass is not conserved during nuclear reactions. An extremely small quantity of mass is converted into energy released during radioactive decay.

During nuclear decay, if the atomic number decreases by one but the mass number is unchanged, the radiation emitted is A.a positron. B.an alpha particle. C.a beta particle. D.a proton.

During nuclear decay, if the atomic number decreases by one but the mass number is unchanged, the radiation emitted is A.a positron. B.an alpha particle. C.a beta particle. D.a proton.

TRANSMUTATION REACTIONS Transmutation - the conversion of an atom of one element into an atom of another element. 2 forms of transmutation 1.Natural Transmutation – occurs when a single unstable radioactive nucleus spontaneously changes by decaying (breaking down). 2.Artificial Transmutation – occurs when a stable nonradioactive nucleus is hit (bombarded) with a high speed particle and is changed to an unstable nucleus. ** Make a T-Chart identifying the differences between natural transmutation and artificial transmutation.

ARTIFICIAL TRANSMUTATION Artificial Transmutation – occurs when a stable nonradioactive nucleus is hit (bombarded) with a high speed particle and is changed to an unstable nucleus. Remember: the ratio of all nuclei with atomic numbers greater than 83 (Bi) makes those nuclei unstable.

Which of the following always changes when transmutation occurs? A.The number of electrons B.The mass number C.The atomic number D.The number of neutrons

A.The number of electrons B.The mass number C.The atomic number D.The number of neutrons Which of the following always changes when transmutation occurs?

BALANCING NUCLEAR EQUATIONS SUPERSCRIPT SUBSCRIPT

BALANCING NUCLEAR EQUATIONS

WRITING DECAY EQUATIONS On Reference Table N, you are given radioisotope symbols and their decay mode. Concept Task : Be able to write or determine a balanced nuclear equation for a radioisotope if its decay mode is known. NOTE: this is generally done by piecing together information from Reference Table N, O, and the P.T. Examples Write nuclear equations for the decay of Pu-239 and I-131.

Examples Write nuclear equations for the decay of Pu-239 and I-131.

PRACTICE PROBLEMS Predict the products of the following nuclear reactions: (a)electron emission by 14 C (b)positron emission by 8 B (c)electron capture by 125 I (d)alpha emission by 210 Rn (e)gamma-ray emission by 56m Ni Complete Practice Problems #33-34 in Topic 12 Note packet

–Half of the radioactive nuclei in the sample decay into new, more stable nuclei. After 1 st half life, (50%) of the original amount of the sample will remain undecayed After a 2 nd half life, (25%) of the original sample will remain undecayed After a 3 rd half life, (12.5%) of the original sample will remain undecayed

PLEASE RETRIEVE YOUR NYS CHEMISTRY REFERENCE TABLE OPEN TO PAGE 6 TABLE N Complete Practice Problems #45-49 on page 234 in Topic 12: Nuclear Chemistry note packet.

SOLVING HALF LIFE PROBLEMS The half-life of Rn-222 (a carcinogenic house pollutant) is 3.8 days. If today your basement contains 20.0 grams of Rn-222, how much will remain after 19 days assuming no more leaks in? You know how much of the isotope you have now, you want to find out how much will be left after a certain amount of time (going into the future). Step 1: Determine how many half-lives have gone by. Take how much time has gone by and divide it by the duration of the half-life. Step 2: Cut the amount (mass, percent, fraction, number of nuclei) in half as many times as there are half lives.

HALF-LIFE Exponential Decay Function A stands for the amount remaining. A 0 stands for the initial amount. n stands for the number of half-lives. You can use the following equation to calculate how much of an isotope will remain after a given number of half-lives. A = A 0  1 2 n

Using Half-Lives in Calculations Carbon-14 emits beta radiation and decays with a half-life (t) of 5730 years. Assume that you start with a mass of 2.00 × 10 – 12 g of carbon a.How long is three half-lives? b.How many grams of the isotope remain at the end of three half-lives?

The half-life of phosphorus-32 is 14.3 days. How many milligrams of phosphorus-32 remain after days if you begin with 2.5 mg of the radioisotope? n = days × = 7 half-lives 1 half-life 14.3 days = (2.5 mg) = 2.0 × 10 –2 mg A = A 0 = (2.5 mg) ( ) 1212 n

Complete Practice Problems #50-55 on page 235 in Topic 12: Nuclear Chemistry note packet.

SOLVING HALF LIFE PROBLEMS The half-life of Tc-99m* (used to locate brain tumors) is 6.0 hours. If 10. micrograms are left after 24 hours, how much Tc- 99m was administered originally? You know how much of the isotope you have now, you want to find out how much there was a certain amount of time ago (going into the past). Step 1: Determine how many half-lives have gone by. Take how much time has gone by and divide it by the duration of the half-life. Step 2: Double the amount(mass, percent, fraction, number of nuclei) as many times as there are half-lives.

Complete Practice Problems #64-71 on page 237 in Topic 12: Nuclear Chemistry note packet.

SOLVING HALF LIFE PROBLEMS A radioactive sample is placed next to a Geiger counter and monitored. In 20.0 hours, the counter’s reading goes from 500 counts per minute to 125 counts per minute. How long is the half- life? You want to find out how long the half-life is, knowing how much a sample has decayed over a given amount of time. Step 1: Determine how many times you can cut your original amount in half in order to get to your final amount. This is the number of half-lives that have gone by. Step 2: Divide the time that has elapsed by the number of half-lives that have passed.

Complete Practice Problems #56-63 on page 236 in Topic 12: Nuclear Chemistry note packet.

Half-lives can be as short as a second or as long as billions of years. Half-Lives of Some Naturally Occurring Radioisotopes IsotopeHalf-lifeRadiation emitted Carbon × 10 3 years  Potassium × 10 9 years  Radon days  Radium × 10 3 years  Thorium days  Uranium × 10 8 years  Uranium × 10 9 years  Comparing Half-Lives HALF LIFE

HALF-LIFE Comparing Half-Lives The age of uranium-containing minerals can be estimated by measuring the ratio of uranium- 238 to lead-206. Because the half-life of uranium- 238 is 4.5 × 10 9 years, it is possible to use its half-life to date rocks as old as the solar system. Uranium-238 decays through a complex series of unstable isotopes to the stable isotope lead-206.

Uranium compounds are found in rocks and in soils that form from these rocks. How can these uranium compounds lead to a buildup of radon in homes and other buildings? Radon gas is a product of the decay of uranium. As the uranium compounds in the soil beneath homes and buildings decay, radon is produced and seeps into the structure.

HALF-LIFE Radiocarbon Dating Plants use carbon dioxide to produce carbon compounds, such as glucose. The ratio of carbon-14 to other carbon isotopes is constant during an organism’s life. When an organism dies, it stops exchanging carbon with the environment and its radioactive C atoms decay without being replaced. Archaeologists can use this data to estimate when an organism died. 14 6

The oldest rocks on Earth have been found to contain 50% U-238 and 50% Pb-206 (what does U-238 ultimately decay into.) What is the age of these rocks? Radioactive dating: used to determine the age of a substance that contains a radioactive isotope of known half-life. Step 1: Determine how many times you can cut your original amount in half in order to get to your final amount. This is the number of half-lives that have gone by. Step 2: Multiply the number of half-lives by the duration of a half-life (found on Reference Table N). HALF-LIFE Radiocarbon Dating

Radioactive IsotopeUse C-14 Used to determine the age of biological remains (archaeology) I-131 Used to detect and cure hyperthyroidism (overactive thyroid) Co-60 Used as a source of radiation for radiotherapy of cancer Tc-99m Used to image blood vessels, especially in the brain, to detect tumors Pu-239 Used as a highly fissionable fuel source to nuclear power or nuclear weapons Am-241 Used in tiny amounts in smoke detectors as a source of ions to make a current U-235 Used as fissionable fuel source for nuclear power or nuclear weapons U-238 Used to determine the age of uranium-containing rock formations (geology)

DECAY SERIES During a decay series, a radioactive nucleus continuously decays by releasing alpha and beta particles until a stable nucleus is produced. Uranium-238 decay series is one of the most common decay series. At the end of the decay series, uranium-238 will decay to lead-206 (a stable nucleus/ Atomic # 82).

DECAY SERIES The graph shows the decay series of Th-230. Each decay by alpha or beta leads to a new isotope until a stable Pb-206 isotope is produced. Complete Practice Problem #21 in Topic 12: Nuclear Chemistry Note Packet. Nuclear Decay Series Worksheet1

FRACTION REMAINING ½ LIFE Fraction remaining expresses the remaining mass of a radioisotope in terms of ratio. Fraction remaining of a radioisotope can be calculated when certain information is known of a decaying process. 1.Fraction Remaining from number of half-life periods (n) 2.Fraction remaining from length of time (t) and half-life (T)

FRACTION REMAINING ½ LIFE

Complete Practice Problems #72-79 on page 238 in Topic 12: Nuclear Chemistry note packet.

IDENTIFYING RADIOISOTOPES When certain information about a decaying process is known, you can identify which radioisotope on Table N the information is referring. Keep the following in mind when comparing the isotopes given as choices Decays to greatest extent Shortest half-life Decays to least extent Longest half-life Smallest remaining % Shortest half-life Smallest mass Largest remaining % Longest half-life Greatest mass Answer Practice Problems #80-82 in Topic 12 note packet, pg239

FISSION VS FUSION

FISSION When the nuclei of certain isotopes are bombarded with neutrons, the nuclei split into smaller fragments. U Uranium-235 (fissionable) U Uranium-236 (very unstable) Ba Barium Kr Krypton n 1010 Neutron More neutrons are released by the fission. These neutrons strike the nuclei of other uranium-235 atoms, which causes a chain reaction.

FISSION In a chain reaction, some of the emitted neutrons react with other fissionable atoms, which emit neutrons that react with still more fissionable atoms.

FISSION Nuclear fission can release enormous amounts of energy. The fission of 1 kg of uranium-235 yields an amount of energy equal to that produced when 20,000 tons of dynamite explode. An atomic bomb is a device that can trigger an uncontrolled nuclear chain reaction. Nuclear reactors use controlled fission to produce useful energy.

FISSION A large fissionable (splittable) nucleus absorbs slow moving neutrons –The large nucleus is split into smaller fragments, with release of more neutrons Tons of nuclear energy is released. Energy is converted from mass. –Energy released is less than that of fusion reactions In nuclear power plants, the fission process is well controlled. –Energy produced is used to produce electricity In nuclear bombs, the fission process is uncontrolled –Energy and radiations released are used to cause destruction Nuclear wastes are also produced. –Nuclear wastes are dangerous and pose serious health and environmental problems –Nuclear wastes must be stored and disposed of properly

FUSION Occurs when nuclei combine to produce a nucleus of greater mass. The energy emitted from the sun involves nuclear fusion Hydrogen nuclei (protons) fuse to make helium nuclei. The reaction also produces two positrons.

FUSION Fusion reactions, in which small nuclei combine, release much more energy than fission reactions, in which large nuclei split apart and form smaller nuclei.

FUSION Two small nuclei are brought together under extremely high temperature and pressure –The two nuclei are fused (joined) to create a slightly larger nucleus Tons of nuclear energy are released. Energy is converted from mass. –Energy released is much greater than that of fission reaction. Fusion produces no nuclear waste, unlike fission Energy from the sun is due to fusion reactions that occur in the core of the sun. High temperature and high pressure are required for a fusion reaction to occur. –High temperature and pressure are necessary to overcome the repelling force of the two positive nuclei that are to be fused –Recall that the nucleus is positively charged. In fusion, two positive nuclei must be brought (joined) together. Opposites attract, BUT like charges repel. Therefore, extremely high temperature and pressure are needed to make two positively charged nuclei join together in a fusion reaction.

Choose the correct words for the spaces. In solar fusion, _______ nuclei fuse to form _______ nuclei. Hydrogen nuclei fuse to form helium nuclei.

FISSION & FUSION Answer Practice Problems #24-27 in Topic 12: Nuclear Chemistry note packet. Pg FUSION FUSSION