![History of the Atom ,[object Object],[object Object]](https://image.slidesharecdn.com/mod13historyofatomparta-100112122838-phpapp02/85/Mod-13-History-Of-Atom-Part-A-1-320.jpg)
![“ To understand the very large, we must understand the very small.” Greek Model Democritus’s model of atom No protons, electrons, or neutrons Solid and INDESTRUCTABLE No experiments to support idea ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],DEMOCRITUS (400 BC) – First Atomic Hypothesis](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
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- 3. DALTON’S ATOMIC THEORY I spent my lifetime trying to figure out how things combine, and now every sixth grader in the universe knows this stuff. John Dalton was the first to make the connection between atomism and recent discoveries in the lab. He used the theory that there were small, indivisible atoms to explain the law of definite proportions and the law of conservation of matter.
- 5. Thomson Model of the Atom J. J. Thomson - English physicist. 1897 Made a piece of equipment called a cathode ray tube. It is a vacuum tube - all the air has been pumped out.
- 6. Thomson’s Experiment + - Metal Disks Voltage source
- 13. Lead block Uranium Gold Foil Flourescent Screen Rutherford “shot” alpha particles (a type of radiation that is made of a helium nucleus of 2 protons and 2 neutrons) at a thin piece of gold foil.
- 16. Because
- 17. Because, he thought the mass was evenly distributed in the atom
- 18. What he got
- 20. +
- 22. Bohr’s Model Nucleus Electron Orbit Energy Levels
- 24. Development of Atomic Models Rutherford model In the early twentieth century, Rutherford showed that most of an atom's mass is concentrated in a small, positively charged region called the nucleus. Bohr model After Rutherford's discovery, Bohr proposed that electrons travel in definite orbits around the nucleus. Thomson model In the nineteenth century, Thomson described the atom as a ball of positive charge containing a number of electrons. Quantum mechanical model Modern atomic theory described the electronic structure of the atom as the probability of finding electrons within certain regions of space.
- 25. Review Models of the Atom Dalton proposes the indivisible unit of an element is the atom. Copyright © 2007 Pearson Benjamin Cummings. All rights reserved. Thomson discovers electrons, believed to reside within a sphere of uniform positive charge (the “plum-pudding model). Rutherford demonstrates the existence of a positively charged nucleus that contains nearly all the mass of an atom. Bohr proposes fixed circular orbits around the nucleus for electrons. In the current model of the atom, electrons occupy regions of space (orbitals) around the nucleus determined by their energies.
Notas do Editor
- Objectives: To describe the Thomson plum-pudding model of the atom. To state the relative charge on an electron and a proton.
- J.J. Thomson (1856 - 1940) proposed a model of the atom with subatomic particles (1903). This model was called the plum-pudding or raisin pudding model of the atom . (Sir Joseph John) J. J. Thompson was born in Manchester in 1856. His father was a bookseller and publisher. Thompson was Cavendish Professor of experimental physics, Cambridge University from 1894 - 1919. He was described as humble, devout, generous, a good conversationalist and had an uncanny memory. He valued and inspired enthusiasm in his students. Thompson was awarded the Nobel Prize for physics for his investigations of the passage of electricity through gases. In 1897, he discovered the electron through his work on cathode rays. Thomson´s son, Sir George Paget, shared the Nobel Prize for physics with C.J. Davisson in 1937. Seven of Thomson´s trainees were also awarded Nobel Prizes. J.J. Thompson is buried in Westminster Abbey close to some of the World’s greatest scientists, Newton, Kelvin, Darwin, Hershel and Rutherford . Thomson won the Nobel Prize in 1906 for characterizing the electron.
- Ernest Rutherford received the Nobel Prize in chemistry (1908) for his work with radioactivity. Ernest Rutherford (1871-1937) was born in Nelson, New Zealand in 1871. He began work in J.J. Thompson ’s laboratory in 1895. He later moved to McGill University in Montreal where he became one of the leading figures in the field of radioactivity. From 1907 on he was professor at the University of Manchester where he worked with Geiger and Marsden. He was awarded the Nobel Prize for Chemistry in 1908 for his work on radioactivity. In 1910, with co-workers Geiger and Marsden he discovered that alpha-particles could be deflected by thin metal foil. This work enabled him to propose a structure for the atom. Later on he proposed the existence of the proton and predicted the existence of the neutron. He died in 1937 and like J.J. Thompson is buried in Westminster Abbey. He was one of the most distinguished scientists of his century. Is the Nucleus Fundamental? Because it appeared small, solid, and dense, scientists originally thought that the nucleus was fundamental. Later, they discovered that it was made of protons (p+), which are positively charged, and neutrons (n), which have no charge.