SCEN103 10/10 Class
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Introduction to Atomic Physics
of first quiz.
- Conductors, insulators, and in-between
- Good conductors -- metals
- copper: 2 x 10-6 ohm-cm
- aluminum: 3 x 10-6 ohm-cm
- iron: 10 x 10-6 ohm.cm
- Bad conductors -- insulators
- glass: 107 -- 109 ohm-cm
- diamond: 108 -- 109 ohm-cm
- rubber: 1011 -- 1013 ohm-cm
- fused quartz: 1014 -- 1016 ohm-cm
- In-between? -- semiconductors
- graphite: 5 x 10-3 ohm-cm
- germanium: 0.1 -- 10 ohm-cm
- silicon: 10 -- 1000 ohm-cm
- Range of resistivities, 22 orders of magnitude, is one of the largest
for physical attributes of matter
- Remember that our goal is to understand digital electronics.
This requires us to understand, in turn:
- integrated circuits, from our understanding of
- transistors, from our understanding of
- semiconductor physics, from our understanding of
- atomic physics.
- Thus our topic of today!
- Atomic structure
- Periodic Table of Elements
- Electrons and nuclei
- Electrons have negative charge, -e
- Protons have same charge, but positive
- Nuclei are comprised of protons and neutrons
- Neutrons have no charge, needed for nuclear stability
- # of electrons = # of protons in undisturbed atom
- hydrogen: 1 electron, 1 proton
- helium: 2 electrons, 2 protons, 2 neutrons for He-4
- copper: 29 electrons, 29 protons, 35 neutrons for Cu-64
- Matter prefers to be electrically neutral.
- Macroscopic separations of positive and negative charges are
- "Unlike charges attract;
Like charges repel."
- So how does the nucleus "stick together" with all those protons in there?
- Mass and size of atom?
- Mass of atom is nuclear
- The mass of a proton is 1836 times that of an electron
- Neutron has almost same mass as proton, slightly larger.
- Can have whatever # of neutrons makes a stable nucleus
-- Different combinations are known as isotopes
-- each with different mass.
- Size of atom is electronic
- Size of nucleus is 10-15 m
- Size of electron cloud is 10-10 m; 100,000 times larger!
- To repeat: Mass is nuclear, size is electronic
- Possible model of atom?
- New Dorito-Toyota model of matter:
Protons and neutrons as Toyotas (2000 pound cars)
surrounded by bags of Doritos (1 pound objects)
-- improve model by spreading out the chips so that the cars cannot be seen,
the so-called Dorito cloud
- Big, fluffy cotton ball with tiny, but heavy, steel BB at center
-- 1 mm BB at 50 yd. line of football field full of fluff
- Refer again to caricature of an atom
- Classification of Solids
- Observe and test the four cylindrical samples provided.
- Try to identify as many physical attributes as possible
-- Be imaginative! I came up with about 10 different properties.
-- Included in each kit are several pieces of abrasive paper and a hard, steel bolt.
- Which classification categories would hold 2 each? which 3:1?
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Last updated Jan. 14, 1998.
Copyright George Watson, Univ. of Delaware, 1996.