![]() Radon has an atomic number of 86, so the parent isotope is represented as Th 86 222Rn. Write the nuclear equation that represents the radioactive decay of radon-222 by alpha particle emission and identify the daughter isotope. When one element changes into another in this manner, it undergoes radioactive decay. Is the parent isotope, and 90 231Th is the daughter isotope. Ĭhemists often use the names parent isotope and daughter isotope to represent the original atom and the product other than the alpha particle. Thus we use subtraction to identify the isotope of the Th atom-in this case, 90 231Th. Moreover, if we lose four nuclear particles of the original 235, there are 231 remaining. If our uranium nucleus loses 2 protons, there are 90 protons remaining, identifying the element as thorium. This means we must have the same number of protons and neutrons on both sides of the nuclear equation. How do we know that a product of this reaction is 90 231Th? We use the law of conservation of matter, which says that matter cannot be created or destroyed. Rather than calling this equation a chemical equation, we call it a nuclear equation to emphasize that the change occurs in an atomic nucleus. We can represent the emission of an alpha particle with a chemical equation-for example, the alpha-particle emission of uranium-235 is as follows: When a radioactive atom emits an alpha particle, the original atom’s atomic number decreases by two (because of the loss of two protons), and its mass number decreases by four (because of the loss of four nuclear particles). (We often use 2 4He to represent an alpha particle.) It has a 2+ charge. An alpha particle is composed of two protons and two neutrons and is the same as a helium nucleus. The first is called an alpha particle, which is symbolized by the Greek letter α. ![]() There are three main forms of radioactive emissions. These emanations were ultimately called, collectively, radioactivity. Further investigations showed that the radiation was a combination of particles and electromagnetic rays, with its ultimate source being the atomic nucleus. He reasoned that the uranium compound was emitting some kind of radiation that passed through the cloth to expose the photographic plate. But in 1896, the French scientist Henri Becquerel found that a uranium compound placed near a photographic plate made an image on the plate, even if the compound was wrapped in black cloth. The two isotopes of hydrogen- 2H and 3H-are given their own names and symbols: deuterium (D) and tritium (T), respectively.Ītomic theory in the nineteenth century presumed that nuclei had fixed compositions. Occasionally, the atomic number is omitted in this notation because the symbol of the element itself conveys its characteristic atomic number. In this case, the mass number is 12, which means that the number of neutrons in the atom is 12 − 6 = 6 (that is, the mass number of the atom minus the number of protons in the nucleus equals the number of neurons). The mass number, the superscript next to the symbol, is the sum of the number of protons and neutrons in the nucleus of this particular isotope. Its atomic number, 6, is the subscript next to the symbol and is the number of protons in the atom. The element in this example, represented by the symbol C, is carbon. We also introduced in Chapter 3 “Atoms, Molecules, and Ions” the notation for succinctly representing an isotope of a particular atom: ![]() Protons and neutrons are located in the nucleus and provide most of the mass of an atom, while electrons circle the nucleus in shells and subshells and account for an atom’s size. We saw in Chapter 3 “Atoms, Molecules, and Ions” that atoms are composed of subatomic particles-protons, neutrons, and electrons. Define and give examples of the major types of radioactivity.
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