Nuclear Chemistry.

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 n0:p+ in a stable atom varies with size Small atoms are stable at a 1:1 ratio As atoms become larger, more n0 are needed for stability. Ratio of n0: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 Rx
Nuclear 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

Types of Radioactive Decay Particles
Stability of a Nucleus An unstable nucleus releases energy by emitting radiation during the process of radioactive decay. Types of Radioactive Decay Particles Particle Mass Charge Symbol Penetrating Power Alpha 4 amu (made of 2 p+ and 2 n0) +2 2 4 He , α Low Beta 0 amu (made of an e-) -1 −1 0 e , β- Moderate Positron 0 amu (made of an anti e-) +1 +1 0 e , β+ Gamma 0 amu None γ High

Alpha Radiation A.K.A Helium nuclei
Each alpha particle contains two protons and two neutrons and has a double positive charge. An alpha particle is written 2 4 He or a. The electric charge is omitted. U 238 92 Uranium-238 Th + 234 90 Thorium-234 He (a emission) 4 2 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. U 238 92 Th + 234 90 He 4 2 → 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).

- 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 1 Neutron p + Proton e –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.

Carbon-14 (radioactive)
Beta Radiation Carbon-14 emits a beta particle as it decays and forms nitrogen-14. C 14 6 Carbon-14 (radioactive) N + 7 Nitrogen-14 (stable) e (b emission) –1 Beta particle → 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.

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.

+ Positron A positron is a particle with the mass of an electron but a positive charge. Its symbol is e . During positron emission, a proton changes to a neutron, just as in electron capture. When a proton is converted to a neutron, the atomic number decreases by 1 and the number of neutrons increases by 1.

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 + 226 88 Radium-226 Th 230 90 Thorium-230 He + g 4 2 Alpha particle Gamma ray → Pa + 234 91 Protactinium-234 Th 90 Thorium-234 e + g –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. Because gamma rays are extremely penetrating, they can be very dangerous. Gamma rays pass easily through paper, wood, and the human body. They can be stopped, although not completely, by several meters of concrete or several centimeters of lead.

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

High penetrating power
Remember

Gamma rays can be dangerous because of their 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.

Nuclear transformations
What determines the type of decay a radioisotope undergoes? 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.

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.

Radioisotopes that undergo beta emission include the following.

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.

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. Most of them emit alpha particles. Alpha emission increases the neutron-to-proton ratio, which tends to increase the stability of the nucleus.

In alpha emission, the mass number decreases by four and the atomic number decreases by two.

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.

Transmutation reactions
Transmutation - the conversion of an atom of one element into an atom of another element. 2 forms of transmutation Natural Transmutation – occurs when a single unstable radioactive nucleus spontaneously changes by decaying (breaking down). 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. Natural Transmutation – Spontaneous. Artificial Transmutation – Deliberate

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

Balancing Nuclear Equations
A nuclear equation is balanced when the sum of masses (superscripts) and sum of charges (subscripts) are equal on both sides of the equation. Rn  2 4 He Po A nuclear equation is balanced because: The mass numbers (superscripts) on the left (222) is equal to the sum of the masses on the right (4+218=222) The charges (subscripts) on the left (86) is equal to the sum of the charges on the right (2+84=86) SUPERSCRIPT SUBSCRIPT

Balancing Nuclear Equations
An unbalanced nuclear equation is usually given as an incomplete equation in which the missing particle must be determined. Examples: 18 37 Ar + −1 0 e  X Top (mass) number of X (37) must equal sum of 0+37 = 37 Bottom (charge) number of X (17) must equal sum of 18+-1=17 X is Cl Complete Practice Problems #28-32.

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: electron emission by 14C positron emission by 8B electron capture by 125I alpha emission by 210Rn gamma-ray emission by 56mNi Complete Practice Problems #28-44 in Topic 12 Note packet

A half-life ( t 1 2 ) is the period of time that must go by for half of the nuclei in the sample to undergo decay. During one half life period: Half of the radioactive nuclei in the sample decay into new, more stable nuclei. After 1st half life, (50%) of the original amount of the sample will remain undecayed After a 2nd half life, (25%) of the original sample will remain undecayed After a 3rd 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.

The half-life of Rn-222 (a carcinogenic house pollutant) is 3. 8 days
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? # half-lives = time elapsed half−life time = 19 days 3.8 days = 5 half-lives have gone by. So, cut the starting amount (20.0 grams) in half 5 times! 20.0  10.0  5.0  2.5  1.25  0.625g is the final amount left

Half-Life Exponential Decay Function
You can use the following equation to calculate how much of an isotope will remain after a given number of half-lives. A = A0  1 2 n A stands for the amount remaining. A0 stands for the initial amount. n stands for the number of half-lives.

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-14. 1 2 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
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 = (2.5 mg) ( ) 1 2 n 7 ( ) 128

A laboratory sample of P-32 triggers 400 clicks per minute in a Geiger- Mueller counter. How many days will it take for the P-32 to decay enough so that there are only 50 clicks per minute? For this one, you need to find out how many half-lives it takes for the counter to go from 400 to 50 clicks per minute. Cut 400 in half until you get to 50: 400  200  100  50 So, you needed to cut 400 in half THREE times to get to 50, so 3 half-lives have gone by. Now, look up the half-life of P-32 on Reference Table N. It’s 14.3 days. That’s how long each half-life is. If three of these half-lives have gone by: 14.3 days half life × 3 half-lives = 42.9 days to cut 400 counts per minutes down to counts per minute.

Look up the half-life of Ne-19 on Reference Table N: 17.2 seconds.
A cylinder contains 5.0 L of pure radioactive Ne-19. If the cylinder is left to sit for seconds, what percent of out original sample of Ne-19 will remain? Look up the half-life of Ne-19 on Reference Table N: 17.2 seconds. # half-lives = time elapsed half−life time = days 17.2 seconds = 6 half-lives have gone by. When we started, 100% of the sample was pure Ne-19. So, cut 100 in half 6 times to find the percent remaining: 100  50  25  12.5  6.25   % of the original sample is still pure, undecayed Ne-19

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

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.

The half-life of Tc-99m. (used to locate brain tumors) is 6. 0 hours
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? # half-lives = time elapsed half life time = 24 hours 6.0 hours = 4 half lives have gone by. So, double the starting amount (10. micrograms) 4 times? 10.  20.  40.  80.  160. micrograms was the original amount administered. If a patient suffered complications due to overdose, and it is found that the doctor game more Tc-99m than was necessary, the doctor will be in for a bit of trouble. * The “m” indicates “metastable”, which means it only gives off gamma rays, not alpha, beta or positron particles.

A laboratory sample of P-32 triggers 100
A laboratory sample of P-32 triggers 100. clicks per minute in a Geiger-Mueller counter. How many days ago did the P-32 take to decay enough to produce clicks per minute? Find out how many half-lives it takes for the counter to go from 400 to 100 clicks per minute. Cut 1600 in half until you get to 100: 1600  800  400  200  100 You needed to cut 1600 in half FOUR times to get to 100, so 4 half-lives have gone by. Now, look up the half-life of P-32 on Reference Table N. It’s 14.3 days. That’s how long each half-life is. If four of these half-lives have gone by: 14.3 days half life x 4 half-lives = 57.2 days ago, the counter would have read 1600 clicks per minute.

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.

A radioactive sample is placed next to a Geiger counter and monitored
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? First, found out how many half-lives it will take for the counter to go from 500 to 125 counts per minute: 500  250  125 You needed to cut 500 in half TWO times to get to 125, so 2 half-lives have gone by. Half-life = time elapsed # of half−lives = hours 2 half−lives = 10.0 hours per half-life

A sample of pure radioactive isotope is left to decay. After 40
A sample of pure radioactive isotope is left to decay. After 40.0 days, the sample is placed in a mass spectrometer, and it is determined that the sample only 25% of the original isotope remains. How long is the half-life? First, find out how many half-lives it will take for 100% of a sample to decay to 25%: 100  50  25 It takes TWO half-lives for the sample to decay from 100% to 25%. Half-life = time elapsed # of half−lives = days 2 half−lives = 20.0 days per half-life

Half-Lives of Some Naturally Occurring Radioisotopes
Half life Comparing Half-Lives Half-lives can be as short as a second or as long as billions of years. Half-Lives of Some Naturally Occurring Radioisotopes Isotope Half-life Radiation emitted Carbon-14 5.73 × 103 years b Potassium-40 1.25 × 109 years b, g Radon-222 3.8 days a Radium-226 1.6 × 103 years a, g Thorium-234 24.1 days Uranium-235 7.0 × 108 years Uranium-238 4.5 × 109 years

Half-Life Comparing Half-Lives
Uranium-238 decays through a complex series of unstable isotopes to the stable isotope lead-206. 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 × 109 years, it is possible to use its half-life to date rocks as old as the solar system.

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

Half-Life Radiocarbon Dating
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).

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? First, find out how many half-lives have had to go by so that you have gone from 100% U-238 to 50% U-238: 100  50 ONE half-life has gone by Age of sample = # Half-lives x Half-life duration (found on Table N) What is the half-life of U-238, according to Table N? 4.51× years Age of sample = # half-lives x half-life duration 1 half-life x (4.51× years) = 𝟒.𝟓𝟏× 𝟏𝟎 𝟗 years old

An ancient scroll is discovered, and it is found that only 25% of the original concentration of C-14 (a radioactive isotope found in equal concentration in all living beings) remains. How old is the scroll? First, find out how many half-lives have had to go by so that you have gone from 100% C-14 to 25% C-14: 100  50  25 TWO half-lifes has gone by What is the half-life of C-14, according to Table N? years Age of sample = # half-lives x half-life duration 2 half-lifes x (5730 years) = 𝟏𝟏,𝟒𝟔𝟎 years old

Radioactive Isotope Use
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) Many radioactive isotopes are very useful to us!

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 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. Fraction Remaining from number of half-life periods (n) Fraction remaining from length of time (t) and half-life (T)

Fraction Remaining ½ Life

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

When the nuclei of certain isotopes are bombarded with neutrons, the nuclei split into smaller fragments. Fission U Uranium-235 (fissionable) 235 92 Uranium-236 (very unstable) 236 Ba Barium-142 142 56 Kr Krypton-91 91 36 3 n 1 Neutron The figure shows how uranium-235 breaks into two smaller fragments of roughly the same size when struck by a slow-moving 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

Occurs when nuclei combine to produce a nucleus of greater mass.
Fusion 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
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 FISSION FUSION

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