Presentation on theme: "ATOMIC STRUCTURE, NUCLEAR CHEMISTRY & UNIT 6"— Presentation transcript:
1ATOMIC STRUCTURE, NUCLEAR CHEMISTRY & UNIT 6 What is an Atom?ATOMIC STRUCTURE,NUCLEAR CHEMISTRY &UNIT 6
2DemocritusHe asked this question: If you break a piece of matter in half, and then break it in half again, how many breaks will you have to make before you can break it no further?Democritus thought that it ended at some point, a smallest possible bit of matter. He called these basic matter particles, atoms.
3History of the Atom Aristotle – famous philosopher Believed all substances made of 4 elementsBlending these in different proportions to get all substancesFire – hotair – lightEarth – cool, heavyWater – wet
4History of the Atom Late 1700s – John Dalton Teacher who summarized results of his experiments and those of othersCombined idea of elements with that of atoms
5Dalton’s Atomic Theory All matter is made of tiny, indivisible particles call atomsAtoms of the same element are identicalAtoms of different elements combine in whole number ratios to form compoundsChemical reactions involve the rearrangement of atoms. No atoms are created or destroyed.
6AtomsSmallest particle of an element that still retains the properties of that element
7JJ ThompsonIn 1897, Thompson discovered the first component part of the atom: the electron, a particle with a negative electric charge. In 1904, he proposed an initial model of an atom, since nicknamed "Thompsons pudding". He imagined the atom as a sphere full of an electrically positive substance mixed with negative electrons "like the raisins in a cake".
22Millikan’s Experiment X-raysX-rays give some electrons a charge.
23Millikan’s Experiment From the mass of the drop and the charge onthe plates, he calculated the mass of an electron
24Other ParticlesProton – positively charged pieces 1840 times heavier than electrons, discovered by E. GoldsteinNeutron – no charge but the same mass as a proton, by J. ChadwickWhere are these pieces?
25Rutherford’s Experiment Ernest Rutherford – English physicistBelieved in the plum pudding model of the atom
26Rutherford’s Experiment Wanted to see how large the positive particles areUsed radioactivityShot alpha particles at gold foilAlpha particles – positively charged pieces,
27Rutherford’s Experiment When an alpha particle hits a fluorescent screen it glows
29Rutherford’s Experiment He expected the alpha particles to pass through without changing direction very muchBecause…The positive charges were thought to be spread out evenlyNot enough to stop the alpha particles
37Density and the AtomSince most of the particles went through, it was mostly empty spaceBecause the alpha particles turned so much, the nucleus was heavySmall volume, big mass, big densityThe small dense positive area is the nucleus