Plum-pudding model

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

This experiment eliminated the plum pudding model as a possible structure of the atom. But what did an atom look like Rutherford figured that the only way to make alpha particles bounce backward... 

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,... 

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. 

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. 

Thomson s "Plum Pudding" Model of Atomic Structure... 

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. 

Rutherford published the results of these scattering experiments in mid-1909, and it seemed as if publication of the discovery of the nuclear atom would soon follow. But the plum pudding model remained the working model of the atom. Through the rest of 1909 and most of 1910, Rutherford pondered. 

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