Chemistry 25.1

25.1 Nuclear Radiation Marie Curie was a Polish scientist whose research led to many discoveries about radiation and radioactive elements. In 1934 she died from leukemia caused by her long-term exposure to radiation. You will learn about the various types of radiation and their effects.

25.1 Radioactivity Marie Curie (1867-1934) and Pierre Curie (1859- 1906) were able to show that rays emitted by uranium atoms caused fogging in photographic plates. Marie Curie named the process by which materials give off such rays radioactivity. The penetrating rays and particles emitted by a radioactive source are called radiation.

25.1 Radioactivity Nuclear reactions differ from chemical reactions in a number of important ways. In chemical reactions, atoms tend to attain stable electron configurations by losing or sharing electrons. In nuclear reactions, the nuclei of unstable isotopes, called radioisotopes, gain stability by undergoing changes.

25.1 Radioactivity An unstable nucleus releases energy by emitting radiation during the process of radioactive decay.

Types of Radiation What are the three main types of nuclear radiation? 25.1 Types of Radiation Types of Radiation What are the three main types of nuclear radiation?

25.1 Types of Radiation The three main types of nuclear radiation are alpha radiation, beta radiation, and gamma radiation. These three types of radiation deflect differently as they pass between a pair of electrically charged plates. Alpha particles (α) and beta particles (β) are deflected in opposite directions—alpha particles toward the negative plate and beta particles toward the positive plate. Gamma rays are undeflected. Applying Concepts Why are gamma rays not deflected?

25.1 Types of Radiation Alpha Radiation Alpha radiation consists of helium nuclei that have been emitted from a radioactive source. These emitted particles, called alpha particles, contain two protons and two neutrons and have a double positive charge.

25.1 Types of Radiation Beta Radiation An electron resulting from the breaking apart of a neutron in an atom is called a beta particle.

25.1 Types of Radiation Carbon-14 emits a beta particle as it undergoes radioactive decay to form nitrogen-14.

25.1 Types of Radiation Radiation is emitted during radioactive decay. a) Uranium-238 undergoes alpha decay to form thorium-234. b) Carbon-14 undergoes beta decay to form nitrogen-14. Interpreting Diagrams What particle is emitted in each decay process?

25.1 Types of Radiation Radiation is emitted during radioactive decay. a) Uranium-238 undergoes alpha decay to form thorium-234. b) Carbon-14 undergoes beta decay to form nitrogen-14. Interpreting Diagrams What particle is emitted in each decay process?

25.1 Types of Radiation Gamma Radiation A high-energy photon emitted by a radioisotope is called a gamma ray. The high-energy photons are electromagnetic radiation.

25.1 Types of Radiation Alpha particles are the least penetrating. Gamma rays are the most penetrating.

25.1 Types of Radiation

25.1 Section Quiz. 25.1.

25.1 Section Quiz. 1. Certain elements are radioactive because their atoms have more neutrons than electrons. an unstable nucleus. a large nucleus. more neutrons than protons.

25.1 Section Quiz. 2. An unstable nucleus releases energy by emitting radiation. thermal vibrations. a chemical reaction. giving off heat.

25.1 Section Quiz. 3. Which property does NOT describe an alpha particle? 2+ charge a relatively large mass a negative charge low penetrating power

25.1 Section Quiz. 4. When a radioactive nucleus releases a high- speed electron, the process can be described as oxidation. alpha emission. beta emission. gamma radiation.

Nuclear Transformations 25.2 Nuclear Transformations Radon-222 is a radioactive isotope that is present naturally in the soil in some areas. It has a constant rate of decay. You will learn about decay rates of radioactive substances.

Nuclear Stability and Decay 25.2 Nuclear Stability and Decay 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 hold the nucleus together.

Nuclear Stability and Decay 25.2 Nuclear Stability and Decay More than 1,500 different nuclei are known. Of those, only 264 are stable and do not decay or change with time. These nuclei are in a region called the band of stability.

Nuclear Stability and Decay 25.2 Nuclear Stability and Decay A neutron-versus-proton plot of all stable nuclei forms a pattern called the band of stability (shown in red). INTERPRETING GRAPHS a. Identify What do the dots on the graph represent? b. Apply Concepts What is the approximate ratio of neutrons to protons for neodymium, whose atomic number is 60? c. Describe How does the neutron-to-proton ratio change as the number of protons increases?

Nuclear Stability and Decay 25.2 Nuclear Stability and Decay The neutron-to-proton ratio determines the type of decay that occurs. A positron is a particle with the mass of an electron but a positive charge. During positron emission, a proton changes to a neutron.

Nuclear Stability and Decay 25.2 Nuclear Stability and Decay

How much of a sample of a radioisotope remains after each half-life? 25.2 Half-Life How much of a sample of a radioisotope remains after each half-life?

25.2 Half-Life A half-life (t1/2) is the time required for one- half of the nuclei of a radioisotope sample to decay to products. After each half-life, half of the existing radioactive atoms have decayed into atoms of a new element.

25.2 This decay curve shows that during each half-life, half of the radioactive atoms decay exponentially into atoms of another element. INTERPRETING GRAPHS a. Identify What percent of the atoms remains after 1 half-life? b. Describe What percent of the atoms remains after two half-lives? c. Apply Concepts Approximately how many half-lives does it take for 12.5% of the radioisotope to remain?

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Half-Life 25.2 Stable Isotope Uranium-238 decays through a complex series of radioactive intermediates, including radon (Rn) gas. Interpreting Diagrams What is the stable end product of this series? Stable Isotope

25.2 Half-Life The ratio of Carbon-14 to stable carbon in the remains of an organism changes in a predictable way that enables the archaeologist to obtain an estimate of its age. This archaeologist is digging for artifacts. The age of an artifact can often be determined from its measured carbon-14 content.

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Transmutation Reactions 25.2 Transmutation Reactions What are two ways that transmutation can occur?

25.2 The conversion of an atom of one element to an atom of another element is called transmutation. Transmutation can occur by radioactive decay. Transmutation can also occur when particles bombard the nucleus of an atom.

25.2 The first artificial transmutation reaction involved bombarding nitrogen gas with alpha particles. The first artificial transmutation reaction involved bombarding nitrogen gas with alpha particles, as illustrated here. Interpreting Diagrams What particles were formed?

All transuranium elements undergo transmutation. 25.2 The elements in the periodic table with atomic numbers above 92, the atomic number of uranium, are called the transuranium elements. All transuranium elements undergo transmutation. None of the transuranium elements occur in nature, and all of them are radioactive.

25.2 Transuranium elements are synthesized in nuclear reactors and nuclear accelerators. Fermilab is a major accelerator center located in Batavia, Illinois. The main accelerator is a ring that has a radius of 1.0 km.

25.2 Section Quiz.

25.2 Section Quiz. 1. During nuclear decay, if the atomic number decreases by one but the mass number is unchanged, the radiation emitted is a positron. an alpha particle. a neutron. a proton.

25.2 Section Quiz. 2. When potassium-40 (atomic number 19) decays into calcium-40 (atomic number 20), the process can be described as positron emission. alpha emission. beta emission. electron capture.

25.2 Section Quiz. 3. If there were 128 grams of radioactive material initially, what mass remains after four half-lives? 4 grams 32 grams 16 grams 8 grams

25.2 Section Quiz. 4. When transmutation occurs, the ________ always changes. number of electrons mass number atomic number number of neutrons

25.2 Section Quiz 5. Transmutation occurs by radioactive decay and also by extreme heating. chemical reaction. high intensity electrical discharge. particle bombardment of the nucleus.

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