Nuclear Chemistry
Ionizing radiation was discovered by ______in 1895, by passing electric current through an evacuated glass tube and producing continuous X-rays. In 1896, ______found that pitchblende (an ore containing uranium and radium) caused a photographic plate to darken, and demonstrated that this was the result of beta radiation (electrons) and alpha particles being emitted. Pierre and Marie Curie, in 1898 isolated radium and polonium from pitchblende and named the process through which these forms of energy are produced ______. A radioactive atom, or radioisotope, undergoes drastic changes as it emits this energy, called ______; due to the instability of their nuclei. The stability of the nucleus depends on the relative proportion of neutrons to protons as well as the overall size of the nucleus. There are two components to nuclear stability; ______stability , which refers to the potential energy of a nucleus relative to the potential energies of its protons and neutrons, and ______stability , which is based on the probability that the nucleus will undergo radioactive decay.
______is the process by which an unstable nucleus emits radiation in order to lose energy. Ernst Rutherford showed that this process is spontaneous, not requiring the input of energy and eventually results in a stable isotope of a different element from the original radioisotope – this is known as transmutation. These transformations can be produced by bombarding atoms with accelerated protons in particle accelerators, like cyclotrons or the new ______collider located near Geneva. After the discovery of the neutron by ______, Enrico Fermi discovered that nuclear transformations of a greater variety can be achieved by using accelerated ______, This ability to break down the nuclei and produce different atoms disproves Dalton’s theory of indivisible atoms.
Three types of radiation can be emitted during radioactive decay:
1) ______, which consists of helium nuclei, also known as ______and contain two protons and two neutrons and carry a double positive charge
2) ______, which consists of fast moving electrons formed by decomposing a neutron in the atom. The neutron decomposes into a ______, which remains in the nucleus and a ______, the electron, which is released. This particle carries a negative charge (indicated by the subscript –1 and a superscript 0 indicating a virtual lack of mass) 0-1 e
3) ______, which is high energy electromagnetic radiation, often emitted along with alpha or beta radiation by the nuclei of disintegrating radioactive isotopes. Since gamma rays have no mass or charge, their emission does not alter the atomic number or mass number of the atom.
All of the elements with atomic number larger than _____, as well as technetium and promethium have no stable isotopes, are radioactive and thus undergo decay. Most of them emit alpha particles, decreasing the mass number by ____ and the atomic number by _____. In this emission, a small amount of energy associated with radiation is produced while a small quantity of mass is lost.
Every radioisotope has a characteristic rate of decay measured by the time required for one-half of the nuclei of a sample to decay to stable products. This rate is known as the ______and is used to predict amounts in the exponential decay formula A = A0 x (1/2)t/T, in which A= amount remaining; A0 = the initial amount; t = time and T = the half life
There are low levels of radioactive materials present throughout the earth. Elements with an atomic number higher than 92 are known as the ______elements and are radioactive to some degree. As more studies were done, it was found that radiation can cause health issues in two ways. Changes to the body cells, known as ______damage as well as genetic changes, those that involve changes to cellular ______can result from overexposure to radiation. A variety of detection devices have been used to gauge the amount of radiation exposure. The first such detector developed is known as a ______counter and is a cylinder containing a low-pressure gas that when ionized, completes the circuit between two electrodes. Today, it is important to measure human exposure which generally involves film badges worn by those who work with radioactive materials and are checked periodically in a ______counter to determine the dosage the individual has received.
Common uses of radiation include the approximation of the age of a material using the isotope ______; the use of ______such as iodine -123, in medical diagnostics; irradiation of pests in agriculture and sterilization of food and other consumer products by irradiation. In an example of how branches of science often work together, ______; the process of dating the age of wood by counting the tree-rings has been used to verify the half-life of radioactive carbon and to calibrate the system of carbon dating.
When the nuclei of some isotopes are bombarded with neutrons, they undergo ______, the splitting of a nucleus into smaller fragments. This process can unleash large amounts of energy and with the release of additional neutrons as the nucleus fractures, can start a chain reaction. In a controlled chain reaction, the energy can be harnessed and used to produce electricity, like in a nuclear ______. The reaction is sustained using a neutron ______, which surrounds the uranium cylinders to slow down the neutrons, allowing them to be more efficiently captured by the uranium fuel rods. The loss control of nuclear chain reactions, such as what happened at the ______nuclear plant , Pennsylvania and the ______reactor in Russia have made the widespread use of nuclear power an uphill battle in the United States. Contrary to popular belief, the danger from these accidents is not of a nuclear explosion, but just from radioactive materials being released into the atmosphere due to a build-up of heat that cannot be dissipated by the reactor coolant system.
The most vivid example of an uncontrolled nuclear chain reaction is a nuclear bomb, like the one developed in the 1940s by joint research known as the ______Project. Because of the widespread fear of exposure to nuclear radiation, studies have been done to determine the dangers of the various types of radiation. Alpha radiation is the least dangerous, with alpha particles stopped by something as lightweight as ______. ______radiation requires the use of something like metal foil to block the their transmission, while ______, the highest energy radiation is blocked (incompletely) only by something as dense as concrete or lead. All nuclear activity in the USA is governed by the NRC or ______.
Another type of nuclear reaction results when nuclei combine to produce a new nucleus of greater mass. This reaction also requires two beta particles and is known as nuclear ______. This is the type of reaction that occurs in the sun. In solar fusion, hydrogen nuclei fuse to make helium nuclei. The drawback to using fusion as an affordable source of energy production is that it only takes place at extremely high ______.
Before attempting to balance and work the nuclear decay problems, complete the nuclear decay gizmo.
Name: ______Date: ______
Student Exploration: Nuclear Decay
Vocabulary: alpha particle, atomic number, beta particle, daughter product, gamma ray, isotope, mass number, nuclear decay, positron, radioactive, subatomic particle
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
The chart below gives the locations, charges, and approximate masses of three subatomic particles. The approximate mass of each particle is given in universal mass units (u).
Particle / Location / Charge / Approximate massProton / Nucleus / 1+ / 1 u
Neutron / Nucleus / 0 / 1 u
Electron / Orbitals / 1– / 0 u
1. The mass number of an atom is equal to the sum of protons and neutrons in the nucleus.
A helium atom has 2 protons and 2 neutrons. What is the mass number of this atom? _____
2. The atomic number of an element is equal to the number of protons in each atom of the element. All helium atoms have 2 protons. What is the atomic number of helium? _____
Gizmo Warm-up
While most atoms are stable, some are radioactive, which means that they have a tendency to undergo spontaneous nuclear decay. The decay of radioactive atoms generally results in the emission of particles and/or energy.
Several types of nuclear decay can be explored with the Nuclear Decay Gizmo™. On the Gizmo, check that Alpha decay and Uranium are selected.
1. Click Play () and then click Pause () when the alpha particle is clearly visible. What is an alpha particle made of? ______
2. Click Play and observe. Besides the alpha particle, what else is emitted from the nucleus during alpha decay? ______
Gamma rays are energetic electromagnetic waves; they are often emitted in nuclear decay.
Activity A:Alpha decay / Get the Gizmo ready:
· Click Reset ().
· Check that Alpha decay and Uranium are selected. /
Question: How does alpha decay change the nucleus of a radioactive atom?
1. Predict: As you observed in the warm-up activity, an alpha particle consists of two protons and two neutrons. How will the emission of an alpha particle affect the following?
A. The atomic number of the atom: ______
B. The mass number of the atom: ______
2. Calculate: Turn on Write equation. What you see is an equation that shows the original uranium atom on the left. The boxes on the right represent the daughter product—the atom produced by radioactive decay—and the emitted alpha particle.
A. In the top left box, write the mass number of the daughter product and press “Enter” on your keyboard. What is this number? ______
B. In the bottom left box, write the atomic number of the daughter product and press “Enter.” What is this number? ______
C. In the next set of boxes, enter the mass number and atomic number of the alpha particle, which has the same composition as the nucleus of a helium (He) atom. After filling in the boxes in the Gizmo, write the completed equation below:
D. According to your equation, what isotope remains after the alpha decay of
uranium-238? (Note: You can look up element symbols on the periodic table.)
______
3. Check: Turn on Show equation, and click Play. The equation will appear at the end of the animation. Was your prediction correct? ______If not, modify your equation above.
4. Practice: Click Reset, turn off Show equation, and select Polonium. Write an equation for the alpha decay of polonium, and then use the Gizmo to check your answer.
What isotope remains after the alpha decay of polonium-212? ______
5. Practice: Click Reset, turn off Show equation, and select Radium. Write an equation for the alpha decay of radium, and then use the Gizmo to check your answer.
What dangerous gas is produced by the decay of radium-226? ______
6. Practice: Americium-241 is a radioactive isotope used in smoke detectors. Write an equation for the alpha decay of Americium-241 below.
7. Analyze: In each equation, how is the mass number on the left side of the arrow related to the sum of mass numbers on the right side of the arrow? Is this true for atomic numbers?
______
______
8. Summarize: In general, how can you determine the mass number of the daughter product after alpha decay has taken place? How can you determine the atomic number?
______
______
9. Think and discuss: Helium is the second most abundant element in the universe, but it is rare in Earth’s atmosphere. Most of the helium used to fill balloons and blimps must be extracted from Earth’s crust. How do you think this helium formed?
______
______
Activity B:Beta decay / Get the Gizmo ready:
· Click Reset, and turn off Show equation.
· Select Beta decay from the Type of decay menu.
· Check that Carbon is selected. /
Question: How does beta decay change the nucleus of a radioactive atom?
1. Observe: Click Play and watch the animation.
A. What happens to the decaying neutron during beta decay? ______
______
B. What is emitted from the nucleus during beta decay? ______
C. What is the mass number and charge of the emitted particle?
Mass number: ______Charge: ______
2. Predict: During beta decay, a neutron is transformed into a proton and an electron (the beta particle), which is emitted. Gamma rays are often emitted during beta decay as well.
How will beta decay affect the atomic number and mass number of the atom?
______
3. Calculate: Turn on Write equation. Fill in the first set of boxes with the mass number and atomic number of the daughter product and the next set of boxes with the mass number and atomic number of the beta particle. (Note: The atomic number of an electron is -1.)
Check your answer by turning on Show equation and clicking Play. Modify your equation if necessary. What isotope is produced by the beta decay of carbon-14? ______
4. Practice: Turn off Show equation. Fill in the equations for the beta decay of iodine-131 and sodium-24 in the spaces below. Use the Gizmo to check your answers.
Activity C:Protons into neutrons / Get the Gizmo ready:
· Click Reset, and turn off Show equation.
· Select Positron emission.
· Check that Carbon is selected. /
Introduction: A positron is a type of antimatter that is equivalent to an electron. If a positron and an electron meet, they will annihilate one another in a burst of gamma rays.