Mass and positive charge are concentrated in a tiny

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Chemistry for Engineering Students
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Chapter 1 / Exercise 1.52
Chemistry for Engineering Students
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mass and positive charge are concentrated in a tiny fraction of the volume of an atom, which Rutherfordcalled the nucleus. It made sense that a small fraction of the α particles collided with the dense, positivelycharged nuclei in either a glancing fashion, resulting in large deflections, or almost head-on, causing themto be reflected straight back at the source.Although Rutherford could not explain why repulsions between the positive charges in nuclei thatcontained more than one positive charge did not cause the nucleus to disintegrate, he reasoned thatrepulsions between negatively charged electrons would cause the electrons to be uniformly distributedthroughout the atom’s volume.Today it is known that strong nuclear forces, which are much stronger thanelectrostatic interactions, hold the protons and the neutrons together in the nucleus. For this and otherinsights, Rutherford was awarded the Nobel Prize in Chemistry in 1908. Unfortunately, Rutherford wouldhave preferred to receive the Nobel Prize in Physics because he considered physics superior to chemistry.In his opinion, “All science is either physics or stamp collecting.”
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Chapter 1 / Exercise 1.52
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Subsequently, Rutherford established that the nucleus of the hydrogen atom was a positively chargedparticle, for which he coined the name proton in 1920. He also suggested that the nuclei of elements otherthan hydrogen must contain electrically neutral particles with approximately the same mass as the proton.The neutron, however, was not discovered until 1932, when James Chadwick (1891–1974, a student ofRutherford; Nobel Prize in Physics, 1935) discovered it. As a result of Rutherford’s work, it became clearthat an α particle contains two protons and neutrons, and is therefore the nucleus of a helium atom.The historical development of the different models of the atom’s structure is summarized in Figure 1.22.Rutherford’s model of the atom is essentially the same as the modern model, except that it is now knownthat electrons are not uniformly distributed throughout an atom’s volume. Instead, they are distributedaccording to a set of principles described in Chapter 6, "The Structure of Atoms." Figure 1.23shows howthe model of the atom has evolved over time from the indivisible unit of Dalton to the modern viewtaught today.
Figure 1.22A Summary of the Historical Development of Models of the Components and Structure ofthe AtomThe dates in parentheses are the years in which the key experiments were performed.

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