Plum pudding

Thomson, who was from England, used plum pudding with raisins as his analogy. 

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

The plum pudding structure of the atom was short-lived. It was disproved by Ernest Rutherford, one of Thomsons best students. Rutherford was an unlikely scientist. He was born and raised in rural New Zealand, about as far as you can get from the worlds scientific centers. He became interested in science while in elementary school. He did well at it immediately, winning scholarship after scholarship and degree after degree, all in physics or mathematics. At age 23, Rutherford got the job he wanted. He was awarded a fellowship to study at Cambridge. He elected to work with J.J. Thomson at the Cavendish Laboratory, the most advanced physics lab in the world. 

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... 

The last big problem facing early twentieth century physics was Ernest Rutherford s atomic structure. Physicists knew that Rutherford s atom could not exist, but no one could come up with anything better. The man who would resolve this conundrum showed up at Manchester, England, in 1912 to work for Rutherford. Rutherford himself had worked for J.J. Thomson and had disproved Thomson s plum pudding structure of the atom. Now, the new man in Manchester, Niels Bohr, was about to do the same thing to Rutherford. By the end of his career, Bohr would have contributed as much as anyone to understanding Feynman s little particles. Science is a meritocracy. Poor kids can excel and get ahead in the world of science just as easily as the well-heeled. For example. 

Read about the gold foil experiment in your textbook. Describe the plum-pudding atomic model. How did the gold foil experiment show the plumpudding model to be in error Describe the nuclear atomic model that replaced the plumpudding model. 

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 proposed the atom consisted of negative electrons embedded in a positive pool, like raisins in plum pudding. 

The second model aerosol is composed of gray spheres that is, the absorber is incorporated in the nonabsorbing particles rather than separate from them. We might visualize this as small carbon spheres uniformly embedded in plum pudding fashion throughout much larger nonabsorbing spheres. 

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. 

An atom has the shape of a sphere with 10-8 cm radius. In this sphere the protons and electrons are occupied in an arbitrary position. The distribution of electrons through this sphere resembles grapes distributed throughout a cake or plum pudding. 

Discovered the electron. Proposed an atom model which could he described a like a round cake vdth berries, or plum pudding. 

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. 

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