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2010 PHYSICS 002C Lecture 24

2010 PHYSICS 002C Lecture 24 - PHYSICS 002C Lecture 24...

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PHYSICS 002C Lecture 24 May 24, 2010 Serway and Jewett Chapter 29 Atomic Physics Do atoms exist or are they just a concept used for chemical formulae, etc? How can we see these Xe atoms on a copper surface with a scaning tunneling microscope if they are just complex probability amplitude waves? Answer: Because t hey are stuck on the surface and can’t move; their phases are all mixed up with the millions of atoms of the surface and solid. Chap 29.1 Early Models of Atoms Lucretius (94-49 BC) thought atoms were tiny and had different shapes. “All Nature consists of particles and the vacuum in which they move.” Dalton (1805) Law of multiple proportions implies the existence of atoms. Lavoisier (1743-1794) Disproved the phlogiston theory. Priestley Discovery of oxygen. During the 19 th century, evidence for the existence of atoms and knowledge of their properties advanced far beyond Lucretius. Faraday [ Phil. Trans. Roy. Soc. 124 , 77 (1834)] discovered that a certain amount of charge is associated with the production of a certain mass of product by electrolysis. One faraday = 96,519 C is associated with the production of one gram molecular weight of product. Menedleev (1870) arranged the periodic table of elements from the periodicity evident in a plot of atomic volume versus atomic weight, and from the similarity of chemistry for every 8 th element. (Newlands, 1865). Exceptions to the arrangement by weights suggested there was more to learn, eg. Ar [A=39.88] and K [A=39.10], where A is the atomic mass in units where the oxygen atom has A = 16. The atomic masses A are very nearly integral, lending support to Wm. Prout’s suggestion that all the elements are made of hydrogen. However chlorine Cl has a weight of 35.46 so it appeared not so. J. J. Thomson [ Phil. Mag. 44 , 293 (1897)] measured e / m for the electron. R. A. Millikan [1909] measured e via his oil drop experiment. Thus m = mass of H / 1836. Don Eigler and his quantum corral of Xe atoms on a Cu surface. Atomic model of exonuclease eating one strand of DNA. John Dalton and his atoms
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2 Dalton’s atomic theory (1805) 1. Elements are made of tiny particles called atoms. 2. All atoms of a given element are identical. 3. The atoms of a given element are different from those of any other element. 4. Atoms of one element can combine with atoms of other elements to form compounds. A given compound always has the same relative numbers of types of atoms. 5. Atoms cannot be created, divided into smaller particles, nor destroyed in the chemical process. A chemical reaction simply changes the way atoms are grouped together. 6. Atoms combine only in pairs, so water is OH etc. Q : Which of the components of Dalton’s theory did not survive the test of time?
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