Silicon, Circuits, and the Digital Revolution
Introduction to Atomic Physics
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 energetically
- "Unlike charges attract; Like charges repel."
- So how does the nucleus "stick together" with all those protons in there?
Mass and Size of Atoms?
- 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!
- Mass is nuclear, size is electronic
- To repeat: Mass is nuclear, size is electronic
- One more time: 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
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Last updated April 10, 2000.
© George Watson, Univ. of Delaware, 2000.