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Unformatted text preview: fire massive alpha particles at the atoms in thin metal foil alpha particles should pass like bullets straight through soft plum pudding atoms o observation: a few alpha particles ricocheted! o new hypotheses: all of the positive charge and nearly all of the mass of the atom is concentrated in a tiny, incredibly dense 'nucleus', about 10-14 m in diameter electrons roam empty space about 10-10 m across, around the nucleus Composition of the Nucleus o nuclei are composed of "nucleons": protons and neutrons o atomic mass units 1 amu (aka 1 dalton) = exactly 1/12 the mass of a carbon-12 nucleus 1 dalton = 1.67 x 10-24 g Table: Subatomic particles important in chemistry. particle symbol charge mass, kg mass, daltons electron e--1 9.10953 10-31 0.000548 proton p+ +1 1.67265 10-27 1.007276 neutron n 1.67495 10-27 1.008665...
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