7.1 Summary Notes - Early Atomic Models Flashcards
Billiard Ball Model of the Atom
Suggest that atoms are very small, indivisible participles
Raisin Bun (Plum Pudding) Model of the Atom
Developed by J.J. Thomson.
Experimental evidence:
Cathode rays travel in straight lines, are deflected by electric and magnetic fields, produce chemical reactions similar to that of light.
Interpretation of evidence:
Cathode rays must be discrete, charged particles
What are cathode rays?
Beams of electrons produced at the cathode. They are produced using high voltage and a cathode and anode inside a glass tube.
What are properties of cathode rays?
- Travel in straight lines
- deflected by electric and magnetic fields
- produce chemical reactions similar to that of light
What type of particles are cathode rays and what led to this conclusion.
The deflection of cathode rays by electric fields and magnetic fields led to the interpretation that cathode rays are discrete, charged particles
Thomson
Determined the charge to mass ratio (q/m) for cathode rays, and interpreted the fact that the ratio was the same for all materials that the substances all contained electrons.
Planetary (Nuclear) Model of the Atom
Developed by Rutherford.
Experimental evidence: when a beam of alpha particles were aimed at gold foil, most alpha particles went directly through, a few scattered at small angles, very few scattered at large angles.
Interpretation of evidence:
The atom is mostly empty space with an extremely small positive nucleus with electrons orbiting it.
Why is Rutherford’s model invalid?
He interspersed the electrons as circling the nucleus which means that they are undergoing centripetal acceleration, but since centripetal acceleration created an accelerating charge, EMR should be emitted by the electron, meaning that the electrons are losing energy, and should be spiralling into the nucleus.
Page 284
