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29-1Bonding in Molecules

29-1Bonding in Molecules. *When atoms cling together as a single unit to achieve lower energy levels, this is a chemical bond. *Bonds occur as ionic an covalent bonds. *Two non-metals typically bond covalently *A metal and non-metal generally make ionic bonds.

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29-1Bonding in Molecules

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  1. 29-1Bonding in Molecules *When atoms cling together as a single unit to achieve lower energy levels, this is a chemical bond. *Bonds occur as ionic an covalent bonds. *Two non-metals typically bond covalently *A metal and non-metal generally make ionic bonds. *An attraction between two molecules is a VanDer Waals Bond. (or weak bond)

  2. 29-2 Potential-Energy Diagrams for Molecules *See diagram p 891

  3. 29-3 Van der Waals Bonds • Attractions between molecules. • Determine melting/boiling points and physical states. • (strongest) Hydrogen bond is 5% of a molecular bond. • Dipole interactions involve +/- ends of molecules sticking together. • Dispersion forces are attractions because of electron movement caused magnetic attractions.

  4. 29-4 Vibrational Energy in Hydrogen See practice problem 29-3 p899

  5. 29-5 Bonding in Solids • Some materials are amorphous. • Many solids are crystalline and have a interconnected structure called a lattice. See page 901 • Important Strong Bonds • Ionic…an electron is stolen giving +/- ions • Covalent…electrons are shared causing attraction • Metallic…electrons shared as a free-moving sea of electrons.

  6. 29-6 Band Theory of Solids • When atoms come together, they form layers we call bands. • For a good conductor, the highest or valence band is only partially filled and the conduction band is close or connected along side it. Electrons jump from hole to hole along the conductor. • For an insulator, the conduction space or band is located fare away, separated by an energy gap. • For a Semiconductor, the separation is smaller than the insulator.

  7. 29-7 Semiconductor Doping • Germanium and Silicon only acquire useful properties for electronics when they are treated with impurities, or doped. • An arsenic doped silicon crystal is called an n-type semiconductor because negative charges carry the electric current. • If a small amount of a 3-electron valence atom, such as gallium is added, a p-type semiconductor is formed, because positive holes seem to carry the charge.

  8. 29-8 Semiconductor Diodes • In a PN junction diode, a few electrons from the n-side cross to the p-side causing a potential difference…. • If the diode is connected forward biased, with positive to p, current flows. If it connected reverse biased, then no current flows. • Since a p-n junction diode only allows electricity to flow one way, it can serve as a rectifier. See page 908 • A half-rectifier with a capacitor can change AC to DC

  9. Light emitting diodes • Solar cells

  10. 29-9 Transisters and Integrated Circuits NPN transistors and PNP transistors serve as amplifiers see page 909

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