CHEM1A_ CH 2 ATOMS, IONS, AND MOLECULES_ THE BUILDING BLOCKS OF MATTER.pdf

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CH 2 ATOMS, IONS, AND MOLECULES: THE BUILDING BLOCKSOF MATTERHistory- Important PeopleDimitri Mendeleev (1870)Taught chemistry at St. Petersburg Technological Institute in RussiaGoal was to teach chemistry systematically, so created periodic tableMendeleev’speriodic tableOrdered elements by increasing atomic mass (protons not discovered yet, so notordered by atomic number)Elements in the same columns had the same periodic properties (similar chemical andphysical properties)Empty spaces left open for elements not yet discoveredWhat Mendeleev didn’t know aboutAtoms, nucleus, and electronsMoles (devised approximate masses from relative ratios, but didn’t know about molarmass)J. J. Thomson (1897)Cathode ray tube experimentDiscovered the electronDiscovered mass-to-charge ratio but neither mass nor chargeEither the mass was really small or charge was really largeElectrodes within a glass tube are attached to the poles of a high-voltage power supplyCathode (-)- an electrode connected to the negative terminal of the power supplyAnode (+)- an electrode connected to the positive terminal of the power supplyWhen these connections are made, electricity travels the length of the glass tube in theform of cathode rays that flow from the cathode to the anodeBeams from cathode ray tube was deflected toward upwards by the electric field towardsthe positively charged plateBeams from cathode ray tube was deflected downwards by the magnetic field when twomagnets were placed at the sides of the tubeThe behavior (deflections) revealed that cathode rays are charged particles ofmatter, not rays of energyThe direction of the deflection revealed that the charges of the cathode rays werenegativeThe deflection pattern and mass-to-charge ratio was always the same no matter whatcathode material was used to generate the particle beams

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