Unit 3 ­ Structures and Properties
Early Theories of the Atom
1) 300 BC ­ Greek philosophers: “_________________” ­ Cut matter into smaller and smaller pieces until you reach a point where it can no longer be divided.
The Greeks coined the term ________, meaning "indivisible"
2) 1805 ­ Dalton’s ‘Billiard ball model’:
"Matter is composed of indestructible and indivisible atoms, which are identical for an element but differ between elements."
Diagram:
3) 1897 ­ Thompson’s ‘Plum Pudding model’ model: supported the discovery of ______________________________ ( ___ and __ ) in the atom. Diagram: He stated the kind of element depended on the number of electrons.
4) 1911 ­ Rutherford’s model: Famous "gold foil" experiment. Diagram of the experiment
Conclusions: Since a few of the alpha particles ___________________...
1) most of the __________ of an atom (protons + neutrons) was concentrated in the center in a tiny area (___________) Since most of the alpha particles went through.
2) the electrons surrounded the nucleus in a __________________________ (occupying most of the volume) 1
Rutherford also determined the mass of a proton to be __________ that of an electron and that in elements the # p+ = # e­
His student, James Chadwick, determined that the mass properties of isotopes was due to ___________________________________.
Problem with Rutherford’s model: 1) Electrons moving freely around the nucleus are constantly changing direction (therefore accelerating). 2) It was well established that moving electrons produce some sort of light (electromagnetic radiation) & are therefore ________________
3) The electrons in an atom (losing energy and emitting light) would _________ _____________________________________________.
Diagram:
But: most matter is stable and is not in danger of collapsing. The revolutionary ideas of the quantum theory were also challenging Rutherford’s model.
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