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The Structure of the Atom

The Structure of the Atom. 3.2. Experiments. Atom – the smallest part of an element that retains the chemical properties of that element. Subatomic particles – p + , n 0 , e -. The Electron. First discoveries – late 1800’s

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The Structure of the Atom

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  1. The Structure of the Atom 3.2

  2. Experiments • Atom – the smallest part of an element that retains the chemical properties of that element. • Subatomic particles – p+, n0, e-

  3. The Electron • First discoveries – late 1800’s • Pass electric current thru a tube of gas at low pres. called “cathode ray tube.” • Opposite side glowed – thought to be b/c of cathode rays and traveled from cathode (-) to the anode (+) • Rays were deflected from magnetic field just like wire carrying ele. current (which are known to be negative)

  4. The Electron • JJ Thompson • Experiments in 1897 measured ratio of charge particles to their mass • Same for all gas or metal combo • Conclusion = cath. rays are composed of all the same particles called electrons • Cathode Ray Tube Video

  5. The Electron • Thompson experiment proves that atoms can be broken down and that e-’s exist. • Has a large charge to mass ratio • Charge = -1.602 x 10-19 couloumbs • Mass 9.109 x 10-31 kg (1/1837 the mass of the simplest H atom)

  6. Inferences from Experiment • Atoms are electrically neutral = there must be a + charge • There must be other particles b/c of weight • Model proposed = plum pudding

  7. Atomic Nucleus • Rutherford’s gold foil experiment • Bombard with α particles (+ charge and 4x mass of H atom) • Some particles were deflected (1 in 8000) • “as if you had fired a 15-inch artillery shell at a piece of tissue paper and it came back and hit you”

  8. Atomic Nucleus • Conclusion • There must be some force within the atom that deflected the particles. • There is a densely packed mass with a + charge • Very small nucleus – like a marble in a football stadium • Gold Foil Experiment

  9. Atomic Nucleus • Protons and neutrons • Mass of a proton = 1.673 x 10-27kg (quite heavier than an e-) • Mass of neutron = 1.675 x 10-27 kg • Nucleus differs in # of p+ and n0 which identifies that type of atom

  10. Atomic Nucleus • Like repels like, but • Up to 83 protons can exist together in a stable nucleus • Nuclear forces – short range forces that hold the particles of the nucleus together

  11. Atomic Size • Electron cloud (of – charge) • Atomic radius ranges b/t 40 and 270 pm (1 pm = 10-12 m) • Atomic nuclei is about 0.001 pm • Very high mass to volume ratio = density of about 2x 108 metric tons/cm3

  12. Assignment • Complete the Section Review on page 76 and do numbers 1-5. This is to be turned in by the end of class.

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