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Intermolecular Forces

Intermolecular Forces. What Holds A Liquid Or Solid Together?. In ionic compounds, all atoms are equally bonded together in the crystal What about covalent?. Two Types of Covalent Compounds. Covalent Network Crystal - all atoms covalently bonded together equally - very strong and hard

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Intermolecular Forces

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  1. Intermolecular Forces

  2. What Holds A Liquid Or Solid Together? • In ionic compounds, all atoms are equally bonded together in the crystal • What about covalent?

  3. Two Types of Covalent Compounds • Covalent Network Crystal - all atoms covalently bonded together equally - very strong and hard - ex: diamond, graphite

  4. Covalent Molecular Substance - individual molecules attracted to one another through intramolecular forces - not anywhere near as strong as networks - ex: water

  5. Intermolecular Forces • Force of attraction between molecules in a covalent molecular substance • Three types: Dipole – Dipole forces Hydrogen Bond London Dispersion forces

  6. Dipole- Dipole • Between polar molecules • Positive pole of one ion attracted to the negative pole of another

  7. Hydrogen Bonding • Attraction between hydrogen atom in one molecule and an unshared pair of electrons on the atom of another molecule

  8. London Dispersion or Van der Walls Force • Hold non-polar molecules together • Caused by motion of electrons

  9. Strength of Interaction • Substances held together by ionic bonds or covalent network bonds are very rigidly connected: mostly solid at room temp and melt at very high temps • Those held by dipole-dipole or hydrogen bonds are fairly strongly connected: liquid at room temp or solids that melt at low temps • Those held by london dispersion forces are weakly connected: gases at room temp; need to be very cold to become liquid

  10. Ionic Covalent Molecular Melting Point High Low Vaporize No Maybe Crystalline Yes, hard & brittle Maybe, soft Dissolve in Water Yes Mostly no Conduct electricity when liquid Yes No Conduct electricity when dissolve in water Yes No Ionic vs. Covalent

  11. Example Substance A melts at 600oC, dissolves well in water, and does not conduct electricity when solid but does when dissolved in water. Is the substance held together by ionic or covalent bonds?

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