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Summarizing Intermolecular Forces

Summarizing Intermolecular Forces. Arrange the following according to increasing melting point. Kr I 2 O 2 He. O 2 < He < I 2 < Kr He < O 2 < I 2 < Kr He < O 2 < Kr < I 2 I 2 < Kr < O 2 < He I 2 < Kr < He < O 2. Hint:

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Summarizing Intermolecular Forces

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  1. Summarizing Intermolecular Forces

  2. Arrange the following according to increasing melting point. Kr I2 O2 He • O2 < He < I2 < Kr • He < O2 < I2 < Kr • He < O2 < Kr < I2 • I2 < Kr < O2 < He • I2 < Kr < He < O2 Hint: All species are nonpolar then check the polarizability

  3. Arrange the following according to increasing melting point. Kr I2 O2 He • O2 < He < I2 < Kr • He < O2 < I2 < Kr • He < O2 < Kr < I2 • I2 < Kr < O2 < He • I2 < Kr < He < O2

  4. Arrange the following according to increasing melting point. MgO CO2 O2 H2O • MgO < H2O < CO2 < O2 • O2 < CO2 < H2O < MgO • O2 < H2O < CO2 < MgO • H2O < O2 < MgO < CO2 • O2 < CO2 < H2O < MgO

  5. Arrange the following according to increasing melting point. MgO CO2 O2 H2O • MgO < H2O < CO2 < O2 • O2 < CO2 < H2O < MgO • O2 < H2O < CO2 < MgO • H2O < O2 < MgO < CO2 • O2 < CO2 < H2O < MgO

  6. 3) Some Properties of Liquids

  7. Intermolecular Forces Affect Many Physical Properties The strength of the attractions between particles can greatly affect the properties of a substance or solution.

  8. Viscosities of a series of hydrocarbons at 20 oC (F/A)t Viscosity • Resistance of a liquid to flow is called viscosity. • It is related to the ease with which molecules can move past each other. • Viscosity increases with stronger intermolecular forces and decreases with higher temperature. SAE 40 SAE 10 Viscosity of motor oil The higher the number the greater the viscosity is at a given temperature SAE: Society of Automotive Engineers

  9. Why certain insects can walk on water? The surface of water behaves almost as if it had an elastic skin! This behavior is due to an imbalance of intermolecular forces at the surface

  10. Surface Tension Surface tension results from the net inward force experienced by the molecules on the surface of a liquid. Bulk molecules are equally attracted to their neighbors Surface molecules are only attracted inward toward the bulk molecules, thereby reducing the surface area and make molecules at the surface pack closely together This causes the liquid as if it has a “skin” Surface tension is the amount of energy required to increase the surface area of a liquid by a unit amount Stronger intermolecular forces cause higher surface tension Water has a high surface tension because of H-bonding (0.07 J/m2) Hg(l) has an even higher surface tension because of strong metallic bonds between atoms (0.46 J/m2)

  11. Adhesive and Cohesive Forces Cohesive forces: are intermolecular forces that bind molecules to one another, e.g. hydrogen bonding, metallic bonds between atoms. Adhesive forces: are intermolecular forces that bind molecules to a surface.

  12. Cohesive and adhesive forces are at play cohesive forces are greater than adhesive forces, the meniscus is curved downwards where mercury contacts the glass adhesive forces are greater than cohesive forces, the meniscus is U-shaped H2O(l) wets the glass Hg(l) does not wet the glass The meniscus is the shape of the liquid surface

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