Understanding Intermolecular Forces: Polar vs Nonpolar Molecules
This chapter delves into the nature of intermolecular forces that govern the interactions between molecules. It explores the different types of bonds, including ionic, covalent, and metallic bonds, and explains how these lead to varying strength in interparticle interactions. The distinctions between polar and nonpolar molecules are elucidated, highlighting their significance in determining properties like melting and boiling points. The chapter examines key concepts like dipole forces, London dispersion forces, and hydrogen bonding, essential for understanding molecular polarity and its implications in different phases of matter.
Understanding Intermolecular Forces: Polar vs Nonpolar Molecules
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Presentation Transcript
INTERMOLECULAR FORCES Chap. 13: Day 2
Generally strongest “Interparticle” Ionic Bond Ion-ion force Metalic bond Electronic force Generally weaker “intermolecular forces” Covalent bonds Polar molecules Dipole forces Nonpolar molecules London Disperson Induced dipole forces Type of Bond determines Forces
Melting Point Energy needed over come the intermolecular forces between molecules in the solid phase Temperature at which molecules in a solid gain enough potential energy to change position (become L)
Boiling Point Energy needed over come the intermolecular forces between molecules in the liquid phase Temperature at which molecules in a liquid gain enough potential energy to change position (become gas)
Molecular Polarity Molecules will be polar if a) bonds are polar AND • the molecule is NOT “symmetric”
Polar or Nonpolar? Compare CO2 and H2O. Which one is polar?
Polar or Nonpolar? • Consider AB3 molecules: BF3, Cl2CO, and NH3.
Molecular Polarity, BF3 B atom is positive and F atoms are negative. B—F bonds in BF3 are polar. But molecule is symmetrical and NOT polar
Molecular Polarity, HBF2 B atom is positive but H & F atoms are negative. B—F and B—H bonds in HBF2 are polar. But molecule is NOT symmetrical and is polar.
Is Methane, CH4, Polar? Methane is symmetrical and is NOT polar.
Substituted Ethylene • C—F bonds are MUCH more polar than C—H bonds. • Because both C—F bonds are on same side of molecule, molecule is POLAR.
NONPOLAR Molecules What causes the differences in intermolecular forces between molecules? Why do the intermolecular forces vary between nonpolar molecules?
Solid Liquid WHY?
DISPERSION FORCE Nonpolar Molecules
POLAR Molecules Why do the intermolecular forces vary between polar molecules?
Figure 9.15 Molecular Polarity Molecules—such as HCl and H2O— can be POLAR (or dipolar). They have a DIPOLE MOMENT. The polar HCl molecule will turn to align with an electric field.
DIPOLE FORCE Polar Molecules
Why different? liquid gas
SOME POLAR Molecules Have “special” Dipole force with Hydrogen HYDROGEN FORCE or HYDROGEN BOND
HYDOGEN BOND NEED TO BE POLAR H is attached to N, F,orO
Graphing: Intermolecular Forces • See handout • 4 different Families • Boiling point vs period 400 k Boiling point 100 k 2 period 6
