2. 5.1 The Discovery of Atomic Structure PPT 制作者：冯爱珍 资料搜集者：马敏 王妙娟 演讲者： 白 苗

3. 1. William Crooks( 威廉 克 鲁克斯 ), a British chemist who invented the cathode ray tube.He abserved the beam in the tube wdeflected when a magnet was placed near it i1879.He wconvinced that this glowing beam,now called a cathod ray,consisted of charged parrticles..Figure5.3

4. 2. Joseph J.Thomson ( 约瑟 夫.j. 汤姆森 ),a British physicist observed rays travelling from the cathode to the anode in the Crookes gas discharge tube were attracted by the positive plate and repelled by the degative plate in 1897. And he proposed that the rays must be composed of negative charged particles.Figure5.4

5. 3. Eugen Goldstein ( 欧根 · 戈尔德施泰因 ),a German scientist,not only observed the stream of electrons emitted by the cathode in a modified Crooks tube,but also observed positive rays in the region behind the cathode. Figure5.5 By 1904 enough evidence had been collected to suggest that atoms were definitely made up of smaller particles. And Thomson offered an explanation, called the "plum pudding" model of the atom, which later was found to bincorrect,but it provided an explanation of the facts known at that time. Figure 5.6

6. 4. Wilhelm Roentgen( 威廉. 伦琴 ), a German scentist, discovered a new type of ray,one that could travel through walls. He named it X ray in 1895. Figure 5.8 5. Antoine Becquerd( 安托万. 拜克沃德 ), a Frenchman discovered a characteristic property of the element uranium when he studied fluorescence,which later be named by Marie Curie radioactivity.

7. 6. Ernest Rutherford （恩内斯特. 卢瑟福）, a New Zealander, observed that the rays of the radiation were defected in different directions. He also discovered the alpha rays. Figure 5.9 Hans Geiger （汉斯 · 盖革）,Ruyherford’s colleague and Earnest Marsden （恩内斯特. 马斯 登）,a 20-year-old undergraduate student investigated the effect of alpha particles on various thinkness of metal foil under Rutherford’s suggestion. They observed while using a gold foil, most of the alpha particles went through the foil, some were sharply deflected, and a few of them even came directly backwond.

8. It was in 1911, almost two years later, that Rutherford told Geiger that he now knew what the atom looked like.he had concluded that all of the positive charge and virtually all of the mass of an atom are concentrated in its extremely tiny nucleus. That is what caused the alpha particles to be so sharply deflected. Figure 5.11 Rutherford's nudear theory of the atom represents a major step in understanding the structure of the atom.

9. 7. In 1932,the British physicist James Chadwick( 詹姆斯 · 查德威克 ) discoverd the neutron--a particle with nearly the same mass as a proton, but with no electrical charge. Then another unanswered question-- the relationship of mass and charge could now be explained that helium nucleus contains 2 protons and 2 neutrons.

10. Above all, we can conclude that the atom is consists of electron, proton and neutron. And we should contribute the discovery of atomic structure to all the great scientists we had mentioned before.