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Intermolecular Forces

Intermolecular Forces. Chapter 11.2 Pages 385-392. Set-up the following chart in your notes. Forces of Attraction. Intramolecular forces – forces of attraction that hold particles together. chemical bonds – ionic, covalent and metallic are intramolecular forces.

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Intermolecular Forces

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  1. Intermolecular Forces Chapter 11.2 Pages 385-392

  2. Set-up the following chart in your notes

  3. Forces of Attraction Intramolecular forces – forces of attraction that hold particles together. chemical bonds – ionic, covalent and metallic are intramolecular forces. covalent bonds hold the hydrogen and oxygen atoms together – intramolecular Intermolecular forces – forces of attraction between neighboring molecules. there is an attraction between one water molecule and another water molecule, which causes water to be a liquid at room temperature. Intermolecular forces are weaker than intramolecular forces

  4. INTRAMOLECULAR FORCES • Are within a molecule itself such as: • Covalent bonds • Ionic bonds • Metallic bonds

  5. Chemical Bonds Metallic bonds - attractive forces between fixed positive ions and the moving valence electrons in a metal. moving valence electrons + + + + + + + + + fixed positive ions Metallic bonds are strong bonds which is why most metals are solids at room temperature. Ionic bonds are solids at room temperature - very strong bonds. Covalent bonds form molecules. Molecules can be solids, liquids or gases at room temperature.

  6. ORDER OF STRENGTH OF INTRAMOLECULAR FORCES • Metallic – strongest • Ionic • Covalent Network (difference in electronegativity is “0”) • Molecular • Polar • Non-Polar

  7. Bonding in Solids Solid Particles Attraction Properties System Forces Molecular Atoms or (Covalent) Molecules Dispersion Dipole-Dipole Hydrogen Bond Soft, low m.p., poor electrical conductors ice Covalent Atoms Network Covalent Bonds Very hard, high m.p., poor conductors diamond Ionic Ions Ionic Bonds Hard & brittle, high m.p., poor conductors, nonvolatile NaCl Metallic Metal Atoms Metallic Bonding Shiny, malleable, ductile, good conductors Al

  8. What are the intramolecular forces? • Choices to consider are metallic, ionic, covalent, or molecular crystals. • C2H6 __________ • Na2O ____________ • SiO2 ______________ • CO2 ______________ • N2O5 ____________ • NaNO3 ______________ • Al ________________ • C(diamond) _______ • SO2 ________________

  9. INTERMOLECULAR FORCES • Are the forces between one molecule and another • Are weak forces compared to “bonding forces” • Involves the attraction of the electrons of one atom for the protons of another atom • Are called van der Waals forces

  10. KINDS OF van der WAALS FORCES • dipole – ion (dissolving) • dipole – dipole • London dispersion forces (temporary dipole forces) • hydrogen bonding

  11. Dipole – ion forces • Ionic compounds dissociate into cations and anions because water is a polar molecule and the negative end of the water molecule is attracted to the cation and the positive end of the water molecule is attracted to the anion.

  12. Ion Dipole

  13. δ - δ + δ - δ + Dipole-Dipole Forces • Electrostatic attraction between polar molecules

  14. Dipole-dipole Forces The dipole-dipole force is the attraction that the δ+ end of one molecule has for the δ- end of a neighboring molecule. δ+ δ- Cl H δ+ H δ- Cl δ+ Cl δ- H H H Cl Cl δ- δ- Polar molecules form a dipole (one end of the molecule has a partial positive charge and the other end of the molecule has a partial negative charge) because of difference in electronegativity.

  15. δ - δ + Dipole-Induced Dipole • A polar molecule forces a dipole in a nonpolar molecule. • “Likes dissolve likes” - +

  16. Dispersion Distribution of electrons is not always even. When electrons become unevenly distributed the one end of the atom becomes  -(the end with more electrons) and the other end becomes  +. Causing one atom to be attracted to another. Attractive force between the  + of one atom and the  - of a neighboring atom. + - + - This is a very weak intermolecular force.

  17. Dispersion (London) Forces • The random movement of electrons creates temporary dipoles in nonpolar molecules. • These movements occur in all molecules to some extent. + - + -

  18. London Dispersion Forces All of the noble gases are gases at room temperature, however, at extremely low temperatures and/or high pressure, they can be condensed. This indicates that there is some attraction between the particles. Dispersion forces - intermolecular force of attraction between induced or temporary dipoles. atom of neon with uneven distribution of electrons. atom of neon with electron evenly distributed in the electron cloud.

  19. F + - + - Hydrogen Bonding • Dipole-Dipole attraction between hydrogen and a highly electronegative element such as F, O, or N. H

  20. Hydrogen Bonding Hydrogen bond is a dipole-dipole attraction that occurs between molecules containing a hydrogen atom bonded to N, O or F. The difference in electronegativity results in particularly strong dipole-dipole attraction. Water exhibits hydrogen bonding. A hydrogen bond is the strongest of all of the intermolecular forces, which is why water is a liquid at room temperature.

  21. ORDER OF STRENGTH OF INTERMOLECULAR FORCES • hydrogen bonding – strongest • dipole – ion • dipole – dipole • London dispersion forces

  22. Comparing Intermolecular Forces Interacting molecules or ions

  23. Identify the Intermolecular Attraction Forces • NF3 • Dipole-Dipole • C6H6 • London • HCl • Dipole-Dipole • H2 Dispersion (London) • Ne London • C2H4Cl2 Dipole-Dipole • HF Hydrogen (Dipole-Dipole)

  24. What intermolecular forces? • HCl • I2 • CH3F • CH3OH • H2O • H2S • SiO2 • SO2 • Cu • Fe • Kr • CH3OH • CuO • NH3 • CH4 • HCl(g) • NaCl • SiC

  25. Properties affected by intermolecular forces • Boiling point • Retention of volume and shape • Surface tension • Evaporation • Vapor pressure • Viscosity

  26. Properties are affected by forces • Physical properties depend on these forces. The stronger the forces between the particles, • (a) The higher the melting point. • (b) The higher the boiling point. • (c) The lower the vapor pressure (partial pressure of vapor in equilibrium with liquid or solid in a closed container at a fixed temperature). • (d) The higher the viscosity (resistance to flow). • (e) The greater the surface tension (resistance to an increase in surface area).

  27. Surface Tension

  28. Vapor Pressure

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