Inside the atom
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This document discusses the development of atomic structure models from ancient Greek philosophers through Rutherford's experiments. It describes Dalton's atomic theory that matter is made of atoms that cannot be divided further. Rutherford discovered that alpha particles fired at a gold foil occasionally bounced off at large angles, inconsistent with Thomson's uniform sphere model. This led to Rutherford's nuclear model with a small, dense nucleus containing positive charge and most mass, surrounded by electrons in empty space. Later, neutrons were discovered in atomic nuclei.
Inside the atom
- 1. Chapter 3
- 2. Section 1
- 3. Greek philosophers devised a theory of atoms, or tiny particles. Didn’t use experiments Used discussion, debate and reason - no evidence or proof.
- 4. All matter is made up of elements – matter made up of atoms of one kind. EX: Silver – silver atoms
- 5. John Dalton combined the idea of elements with the Greek theory of the atom. Matter is made up of atoms. Atoms cannot be divided into smaller pieces.
- 6. All atoms of an element are exactly alike. Different elements are made of different atoms.
- 7. Dalton’s Theory was tested by William Crooks and his cathode- ray tube experiment. Crooks hypothesized that the green glow in the tube was caused by a stream of particles. Cathode Rays
- 8. Cathode Ray Tube CRT Used in TV and computer screens for many years.
- 9. JJ Thomson discovered negatively charged particles, electrons, which are part of every atom.
- 10. Thomson revised Dalton’s model to include a sphere with a positive charge & negatively charged electrons spread evenly within the positive charge.
- 12. The negatively charged electrons and the positive charge in the sphere neutralized each other.
- 13. Earnest Rutherford tested Thomson’s model. Rutherford and his coworkers began an experiment to find out if Thomson's model of the atom was correct.
- 14. They wanted to see what would happen when they fired fast moving, positively charged bits of matter, called alpha particles, at a thin film of a metal such as gold.
- 15. Alpha particles, which come from unstable atoms, are positively charged, and so they are repelled by particles of matter that also have a positive charge.
- 16. Rutherford was certain he knew what the results of this experiment would be. His prediction was that most of the speeding alpha particles would pass right through the foil and hit the screen on the other side.
- 17. Rutherford was shocked when his student rushed in to tell him that some alpha particles were veering off at large angles.
- 18. The positively charged alpha particles were moving with such high speed that it would take a large positive charge to cause them to bounce back. The uniform mix of mass and charges in Thomson's model of the atom did not allow for this kind of result.
- 19. An atomic model with a nucleus was developed. The positively charged proton is located in a very small space at the center of the atom.
- 20. Most of an atom is empty space occupied by nearly massless electrons. Rutherford's nuclear model was applauded as other scientists reviewed the results of the experiments. However, some data didn't fit.
- 21. Because the atom was only protons and electrons and electrons are “massless” the mass of an atom should have been approximately equal to the mass of its protons.
- 22. It isn’t. The mass of most atoms is at least twice as great as the mass of its protons. It was proposed that another particle must be in the nucleus to account for the extra mass.
- 23. Electrically neutral particles, neutrons, are also located in the nucleus. The number of electrons equals the number of protons in an atom.
- 25. The electron cloud model explains the unpredictable wave behavior of electrons, which could be anywhere in the area surrounding the nucleus. http://www.edumedia- sciences.com/en/a66-electron- distribution
- 26. Explain how the nuclear atom differs from the uniform sphere model of the atom. SC.A.2.3.2 In the nuclear atom, all the positive charge & almost all of the mass are in a tiny nucleus with electrons occupying the space around it. The uniform sphere model stated the atom was the smallest type of matter and the same throughout.
- 27. Determine how many electrons a neutral atom with 49 protons has. SC.A.2.3.2 49 electrons
- 28. Cathode rays are Crookes hypothesized that the greens glow in the tube was caused by rays. They this discovered cause TV and computer have display screens.
- 29. Design and complete a concept map using all the words in the vocabulary list for this section. Add any other terms or words that will help create a complete diagram of the section and the concepts it contains.
- 31. In Rutherford's experiment, why wouldn't the electrons in the atoms of the gold foil affect the paths of the alpha particles? SC.A.2.3.2 Because most alpha particles could move through the foil with little or no interference because of the empty space that makes up most of atom.