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and go straight to the atomic scale used to be wed

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Unformatted text preview: s science, chemistry, condensed matter physics...) and go straight to the atomic scale • Used to be, we’d say you can’t “see” atoms, but now we can! (Atomic Force Microscopy) 4 Atoms can now be “imaged” Image of individual atoms in Mica (from www.di.com, Digital Instruments) Image www.di.com see also http://stm2.nrl.navy.mil/how-afm/how-afm.html see http://stm2.nrl.navy.mil/how-afm/how-afm.html 5 Early Evidence for Atoms Early 1800 John Dalton found that substances combine in 1800 simple ratios of their weights, eg: 2 grams of X for every 4 grams of Y, or 1:1, 1:2, 1:3, 2:3,… This is easy to understand if substances made of atoms Eg Water H2O needs 2 atoms of Hydrogen for one of Oxygen. If we call the mass of one atom of H 1 (atomic mass unit) then Oxygen is 16, and ratio will be 2:16 = 1:8 6 iClicker Question iClicker In Photosynthesis, CO2 and H2O combine. If (for simplicity) we have one molecule of each, what is the mass ratio? H has mass 1 amu, C 12 amu, O is 16 amu a) 28:17, ie 28 amu of CO2 for each 17 of H2O b) 28:18 c) 22:9 d) 1:1 7 Convincing evidence of atoms: Brownian Motion Convincing Pollen grains (and all other...
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