Polar Bonds and Molecules Chapter 8.4

If the difference in electronegativity is between 1.7 to 4.0: Ionic Bond 0.3 to 1.7: Polar Covalent Bond 0.0 to 0.3: Non-Polar Covalent Bond

Electronegativity Scale

Polar Covalent Bond vs Non-Polar Covalent Bond

Polar Covalent vs Non-Polar Covalent

Drawing Polar Bonds and Molecules

Net Dipole of Molecules Dipole – separation of charges within a molecule between two covalently bonded atoms. Net Dipole – When all the dipole vectors are summed to give one overall dipole.

Attractions Between Molecules or Intermolecular Forces (IM Forces)

We have already talked about intramolecular forces. Intramolecular forces hold atoms together in a molecule. Covalent bonds would be an example. Intermolecular forces are attractive forces between molecules.

Intermolecular Forces Intramolecular = strong Intermolecular = weak They do control physical properties such as boiling and melting points, vapor pressure, and viscosity

Types of Intermolecular Forces van der Waals Forces Dipole-dipole interactions Ion-Dipole interactions London dispersion forces

Dipole-Dipole Interactions Molecules that have permanent dipoles are attracted to each other.

Ion-Dipole Interactions Attractive forces between an ion and a polar molecule Ion-Dipole Interaction The larger the charge the stronger the force

London Dispersion Forces Occasionally electrons wind up on the same side of the atom.

London Dispersion Forces At that instant, the helium atom is polar.

London Dispersion Forces This polar helium atom then induces a dipole on a neighboring helium atom.

London Dispersion Forces London dispersion forces, or dispersion forces, are attractions between an instantaneous dipole and an induced dipole.

London Dispersion Forces These forces are present in all molecules, whether they are polar or nonpolar. The tendency of an electron cloud to distort in this way is called polarizability.

Types of Intermolecular Forces Hydrogen Bonding The dipole-dipole interactions experienced when H is bonded to N, O, or F are unusually strong. We call these interactions hydrogen bonds.

Hydrogen Bonding: Water

Hydrogen Bonding: Water