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Ch.6 - Electronic Structure of Atoms
Chapter 6, Problem 110d

The two most common isotopes of uranium are 235U and 238U. (d) 238U undergoes radioactive decay to 234Th. How many protons, electrons, and neutrons are gained or lost by the 238U atom during this process? (e) Examine the electron configuration for Th in Figure 6.31. Are you surprised by what you find? Explain.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Isotopes

Isotopes are variants of a chemical element that have the same number of protons but different numbers of neutrons. For example, uranium-235 (235U) and uranium-238 (238U) are isotopes of uranium, with 235U having 143 neutrons and 238U having 146 neutrons. This difference in neutron count affects their stability and radioactive properties.
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Radioactive Decay

Radioactive decay is the process by which an unstable atomic nucleus loses energy by emitting radiation. In the case of 238U decaying to 234Th, it undergoes alpha decay, where it emits an alpha particle (2 protons and 2 neutrons). This process changes the element into a different one, resulting in a loss of protons and neutrons from the original atom.
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Rate of Radioactive Decay

Electron Configuration

Electron configuration describes the distribution of electrons in an atom's orbitals. It is crucial for understanding an element's chemical properties and reactivity. For thorium (Th), the electron configuration can reveal its valence electrons and how it might bond with other elements, which can be surprising if it differs significantly from its predecessor in the decay process.
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Electron Configuration Example
Related Practice
Textbook Question

The discovery of hafnium, element number 72, provided a controversial episode in chemistry. G. Urbain, a French chemist, claimed in 1911 to have isolated an element number 72 from a sample of rare earth (elements 58–71) compounds. However, Niels Bohr believed that hafnium was more likely to be found along with zirconium than with the rare earths. D. Coster and G. von Hevesy, working in Bohr's laboratory in Copenhagen, showed in 1922 that element 72 was present in a sample of Norwegian zircon, an ore of zirconium. (The name hafnium comes from the Latin name for Copenhagen, Hafnia). (d) Using their electron configurations, account for the fact that Zr and Hf form chlorides MCl4 and oxides MO2.

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Textbook Question

The first 25 years of the twentieth century were momentous for the rapid pace of change in scientists' understanding of the nature of matter. (b) In what ways is de Broglie's hypothesis, as it applies to electrons, consistent with J. J. Thomson's conclusion that the electron has mass? In what sense is it consistent with proposals preceding Thomson's work that the cathode rays are a wave phenomenon?

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Textbook Question

The two most common isotopes of uranium are 235U and 238U. (b) Using the periodic table in the frontinside cover, write the electron configuration for a U atom.

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Textbook Question
(d) Treating bismuth with fluorine gas forms BiF5. Use the electron configuration of Bi to explain the formation of a compound with this formulation.
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