Thomson model of the atom

If the Thomson model of the atom were correct, any a-particles passing through the foil would have been deflected by very small angles. Quite unexpectedly, nearly all of the a-particles passed through the foil with little or no deflection. A few, however, were... 

When Rutherford s coworkers bombarded gold foil with a particles, they obtained results that overturned the existing (Thomson) model of the atom. Explain. 

Describe how the Rutherford a-particle scattering experiment (a) overturned the Thomson model of the atom and (b) led to a conflict with the predictions of classical physics. 

Thomson model of the atom. In this early model of the atom, negative particles (electrons) were thought to be embedded In a positively charged sphere. It Is sometimes called the plum pudding model. 

In the Thomson model of the atom, the electrons are negatively charged particles embedded in the positively charged atomic sphere (see Figure 5.4). A neutral atom could become an ion by gaining or losing electrons. 

Thomson model of the atom Thomson asserted that atoms are not indivisible but are composed of smaller parts they contain both positively and negatively charged particles—protons as well as electrons. [5.6] titration The process of measuring the volume of one... 

The first detailed model of the atom, proposed by J. J. Thomson in 1898, was based upon the expectation that the atom was a sphere of positive electricity in which electrons were embedded like plums in a pudding. This picture of the atom was not particularly satisfying because it was not useful in predicting or explaining the chemical properties of the atom. Finally, in 1911, a series of experiments performed in the McGill University laboratory of Ernest Rutherford showed that Thomson s picture of the atom had to be abandoned. 

The first observation made with this apparatus was that apparently all the alpha particles passed through the foil undeflected. Let us see if this result is consistent with the model of the atom proposed by Thomson. You will recall that Thomson s picture of the atom assumed that the positive charge is distributed evenly throughout the entire volume of the atom with the negative electrons embedded in il. Since the electrons weigh so little, the positive part accounts for nearly all of the mass of the atom. Thus the Thomson model pictures the atom as a body of uniform density. 

Electrons. If the discovery of isotopes threatened ro undermine the periodic system, the discovery of the electron explained many of the periodic properties on which the table was based. J. J. Thomson attempted to explain the periodic system by postulating rings of electrons embedded in the positive charge that made up his phim pudding model of the atom. Thomson s model was quickly superseded by more sophisticated and elaborate mod-... 

The first steps toward the understanding of the nature of the chemical bond could not be taken until the composition and structure of atoms had been elucidated. The model of the atom that emerged from the early work of Thomson, Rutherford, Moseley, and Bohr was of... 

O (a) VU f In what ways did Rutherford s model of the atom differ from Thomson s ... 

Over the centuries, many other concepts were proposed to explain the nature of matter— many of them extensions of the Greek concept of an ultimately indivisible and indestructible elementary bit of matter. But it was not until J. J. Thomson proposed his model of the atom, consisting of a sphere with an agglomeration of particles with negative electric charges somehow positioned randomly inside a very small ball of matter, that the modern structure of the atom began to take shape. 

An overview of a scientific subject must include at least two parts retrospect (history) and the present status. The present status (in a condensed form) is presented in Chapters 2 to 21. In this section of the overview we outline (sketch) from our subjective point of view the history of electrochemical deposition science. In Section 1.2 we show the relationship of electrochemical deposition to other sciences. In this section we show how the development of electrodeposition science was dependent on the development of physical sciences, especially physics and chemistry in general. It is interesting to note that the electron was discovered in 1897 by J. J. Thomson, and the Rutherford-Bohr model of the atom was formulated in 1911. 

In 1910 Rutherford wrote to a friend, I think I can devise an atom much superior to J.J. s, for the explanation of and stoppage of alpha and beta particles, and at the same time I think it will fit in extraordinary well with the experimental numbers. Rather than devise a model of the atom based on theoretical ideas as Thomson had done, Rutherford intended to probe atomic structure by bombarding atoms with particles ejected from radioactive atoms. Rutherford felt that experimental physics was the only real physics and that by performing experiments he could gain greater insight into atomic structure than Thomson had been able to get using only theory. 

Thomson s plum-pudding model of the atom. Thomson proposed that the atom might be made of thousands of tiny, negatively charged particles swarming within a cloud of positive charge, much like plums and raisins in an old-fashioned Christmas plum pudding. 

It was reasoned that if atoms contained negatively charged particles, some balancing positively charged matter must also exist. From this, Thomson put forth what he called a plum-pudding model of the atom, shown in Figure 3-15- Further experimentation, however, soon proved this model to be wrong. 

J. J. Thomson (1856-1940), an English physicist, proposed a plum pudding model of the atom, in which the atom was a diffuse cloud of positive charge (the pudding) negatively charged electrons (the raisins) were embedded randomly in the cloud. 

Joseph John Thomson, often known as J. J. Thomson, was the first to examine this substructure. In the mid-1800s, scientists had studied a form of radiation called "cathode rays" or "electrons" that originated from the negative electrode (cathode) when electrical current was forced through an evacuated tube. Thomson determined in 1897 that electrons have mass, and because many different cathode materials release electrons, Thomson proposed that the electron is a subatomic particle. Thomson s model of the atom was a uniformly positive particle with electrons contained in the interior. This has been called the "plum-pudding" model of the atom where the pudding represents the uniform sphere of positive electricity and the bits of plum represent electrons. For more on Thomson, see http //www.aip.org/historv/electron/iihome.htm. 

By the early twentieth century, chemists and physicists recognized that the atoms of which chemical elements are composed are themselves made up of electrons and protons, of electrically negative and positive subatomic particles that were the universal constituents of all chemical elements. Sir Joseph Thomson had discovered the electron in 1897. Ernest Rutherford postulated the existence of a positive nucleus in atoms in 1911, and he used this in developing his planetary model of the atom, with a positive center and orbiting electrons. He discovered the proton in 1919, in experiments on the disintegration of atomic nuclei. Much later, in 1932, the British physicist James Chadwick (1891— 1974) discovered a third subatomic particle, the electrically neutral neutron. 

The correct answer is (D). Thomson s work with cathode rays led to his eventual discovery of many important properties of the electron and his subsequent development of the plum pudding model of the atom. 

Rutherford described his new model of the atom during a lecture he gave in Cambridge in the fall of 1911. J. J. Thomson listened to the lecture, hut while the alpha-scattering data presented by Rutherford supported a nuclear model, Thomson did not. It may have heen that another physicist, Niels Bohr, also heard this... 

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