Polar Bonds and Molecules

Chapter 8.4

– 1.7 to 4.0: Ionic Bond– 0.3 to 1.7: Polar Covalent Bond– 0.0 to 0.3: Non-Polar Covalent Bond

If the difference in electronegativity is between

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 orIntermolecular Forces (IM Forces)

We have already talked about intramolecular forces.

Intermolecular forces are attractive forces between molecules.

Intramolecular forces hold atoms together in a molecule.

Covalent bonds would be an example.

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

• Dipole-dipole interactions

• Ion-Dipole interactions

• London dispersion forces

van der Waals Forces

Dipole-Dipole Interactions

Molecules that have permanent dipoles are attracted to each other.

Ion-Dipole InteractionsAttractive 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

• 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

Hydrogen Bonding: Water

Hydrogen Bonding: Water