Electrons plum pudding model

Figure 1.2 The plum pudding model of the atom consisted of electrons scattered in a sphere of positive charge.

It was apparent to Thomson that if atoms in the metal electrode contained negative particles (electrons), they must also contain positive charges because atoms are electrically neutral. Thomson proposed a model for the atom in which positive and negative particles were embedded in some sort of matrix. The model became known as the plum pudding model because it resembled plums embedded in a pudding. Somehow, an equal number of positive and negative particles were held in this material. Of course we now know that this is an incorrect view of the atom, but the model did account for several features of atomic structure. 

Rutherford s experiment demonstrated that the total positive charge in an atom is localized in a very small region of space (the nucleus). The majority of a particles simply passed through the gold foil, indicating that they did not come near a nucleus. In other words, most of the atom is empty space. The diffuse cloud of electrons (which has a size on the order of 10 8cm) did not exert enough force on the a particles to deflect them. The plum pudding model simply did not explain the observations from the experiment with a particles. 

In the next few years after the Yale lectures, Thomson came up with several lines of evidence that the mass of an atom is due primarily to its positive charge and that the number of an atom s electrons is substantially smaller than in the plum-pudding model. 127 In addition, Thomson now argued against the existence of intramolecular ions after failing to find evidence that CO, HC1,... 

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. 

It was perhaps Thomson who first suggested a specific structure for the atom in terms of subatomic particles. His plum pudding model (ca. 1900), which placed electrons in a sea of positive charge, like raisins in a pudding., accorded with the then-known facts in evidently permitting electrons to be removed under the influence of an electric potential. The modem picture of the atom as a positive nucleus with extranuclear electrons was proposed by Rutherford13 in 1911. It arose from... 

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. 

J. J. Thomson Plum pudding model charge-to-mass ratio of electron Work with cathode rays discovered the positive and negative nature of the atom also determined the charge-to-mass ratio for electrons... 

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. 

The plum pudding model, a batter of positive charge with minute negative currants embedded in it, appeared to be consistent with experiments which showed that a beam of electrons could pass undeflected through a thin metallic foil. In other words, one might conclude, as Philipp Lenard (1862-1947) did in 1903, that the atom was mostly empty space. These data as well as the larger question about the inner structure of the atom prompted a most provocative line of experimentation by Ernest Rutherford (1871-1937). Manchester University was the site of these historical experiments, which Rutherford initiated soon after he arrived in 1907 to assume his responsibilities as Langworthy Professor of Physics. 

Thomson proposed that the electrons of an atom were embedded in a positively charged ball of matter. His picture of an atom, which is shown in Figure 7, was named the plum-pudding model because it resembled plum pudding, a dessert consisting of a ball of cake with pieces of fruit in it. Ernest Rutherford, one of Thomson s former students, performed experiments in 1909 that disproved the plum-pudding model of the atom. 

Rutherford concluded that the plum pudding model was incorrect because it could not explain the results of the gold foil experiment. He set out to develop a new atomic model based upon his findings. Considering the properties of the alpha particles and the electrons, and the frequency of the deflections, he calculated that an atom consisted mostly of empty space through which the electrons move. He also concluded that there was a tiny, dense region, which he called the nucleus, centrally located within the atom that contained all of an atom s positive charge and virtually all of its mass. Because the nucleus occupies such a small space and contains most of an atom s mass, it is incredibly dense. Just how dense If a nucleus were the size of the dot in the exclamation point at the end of this sentence, its mass would be approximately as much as that of 70 automobiles ... 

FIGURE 2.5 Thomson s model of the atom, sometimes described as the "plum pudding" model, after a traditional English dessert cantaining raisins. The electrons are embedded in a uniform, positively charged sphere. 

By the early 1900s, two features of atoms had become clear they contain electrons, and they are electrically neutral. To maintain electric neutrality, an atom mnst contain an equal number of positive and negative charges. Therefore, Thomson proposed that an atom could be thought of as a uniform, positive sphere of matter in which electrons are embedded like raisins in a cake (Figure 2.5). This so-called plum-pudding model was the accepted theory for a number of years. 

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. 

Joseph John Thomson had supposed that an atom was a uniform sphere of positively charged matter within which electrons were circulating (the plum-pudding model). Then, around the year 1910, Ernest Ruthorford (who had discovered earlier that alpha rays consisted of positively charged particles having the mass of helium atoms) was led to the following model for the atom Protons and neutrons exist in a very small nucleus, which means that the tiny nucleus contains all the positive charge and most of the... 

Thomson devised the famous plum pudding model of the atom, in which electrons were compared to negative plums embedded in a positively charged pudding. The idea was wrong, and his successor at Cambridge, Ernest Rutherford, was soon to develop the nuclear model of the atom. 

One of the early models of the atom was the plum pudding model, in which the electrons were pictured as embedded in a positively charged spherical cloud, much as raisins are distributed in an old-fashioned plum pudding. 

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