Forces of Attraction

Intermolecular Forces

Bonding ForcesForces of attraction that hold atoms together in one structure are intramolecular (inside) forces.metallic (mobile electrons

in a solid)covalent (nonmetals sharing electrons)ionic (separate ions in crystal lattice)

Forces Between ParticlesForces that exist outside a molecule are called intermolecular forces.(+) to

(-) attraction

Intermolecular attractions cause the molecules to align themselves (+) to (-).

Types of IMFsDifferent kinds of particles have different types and strengths of attractions.

F2

(nonpolar)

London Dispersion Force

F2

(nonpolar)

Types of IMFs

Dipole-Dipole Force

CO(polar)

CO(polar)

Attractions between polar molecules are stronger than those between nonpolar molecules.

Types of IMFs

H2O(very polar)

H2O(very polar)

Hydrogen Bond

The strongest attraction between covalent molecules is the hydrogen bond, which occurs between H and N, O, or F only.

Types of IMFsCharged particles (ions) interact with polar molecules to form an even stronger bond.

Na1+

(ion)

H2O

H2O

H2OIon-Dipole Force

Comparison of Forces

Are ions present?

Are polar molecules present?

Ionic Bonds

Ion-Dipole Forces

Are polar molecules present?

Are H atoms

bound to N, O, or

F?Hydrogen

Bonds

Dipole-

Dipole Forces

Dispersion Forces

Only

yes

yes no

no

no no

yes

yes

strength of attraction

IMF ObservationsIntermolecular attractions explain why some substances are solids and others are liquids or gases at the same temperatures.

NaCl is solid

H2O is liquid

Cl2 is gas

At 300K:

IMF ObservationsIons dissolve in water due to the strength of ion-dipole forces pulling apart the ions from the crystal lattice.

Intermolecular Force Practice1) ___________ are always stronger and require more energy to break than ____________.A) dipole-dipole, ion-dipole

B) intermolecular, intramolecular

C) hydrogen bonds, dispersion forces

D) ion-dipole, ionic bonds

Intermolecular Force Practice2) True or False: London Dispersion Forces result from temporary shifts in the electron density of a nonpolar molecule.

Intermolecular Force Practice3) Van der Waals Forces are forces of attraction between covalent molecules. They are divided into:A) dispersion forces,

dipole-dipole forces, and ion-dipole forces

B) dipole-dipole forces, hydrogen bonds, and dispersion forces

C) ionic bonds and hydrogen bonds

D) ion-dipole forces and ionic bonds

Intermolecular Force Practice4) True or False: Hydrogen bonds are intramolecular (bonding) forces.

Intermolecular Force Practice5) A pair of the molecule shown below would likely exhibit which IMF most strongly? A) London dispersion

forcesB) dipole-dipole forcesC) ion-dipole forcesD) hydrogen bonds

O

F F

Intermolecular Force Practice6) A pair of the molecule shown below would likely exhibit which IMF most strongly? A) London dispersion

forcesB) dipole-dipole forcesC) ion-dipole forcesD) hydrogen bonds

H

H

Intermolecular Force Practice7) A pair of the molecule shown below would likely exhibit which IMF most strongly?

A) London dispersion forces

B) dipole-dipole forcesC) ion-dipole forcesD) hydrogen bonds

H HN

H

Intermolecular Force Practice8) When heat is added to solid water, it is observed that the molecules begin to liquefy. What is happening to the molecules?A) The molecules to give off heat

and take up more space as they overcome hydrogen bonds.

B) The molecules move faster and are able to overcome the intermolecular forces.

Intermolecular Force Practice9) Ionic solids typically dissolve into water. This is best explained by:A) Multiple ion-dipole interactions

overcome the force of attraction between ions.

B) Hydrogen bonds between ions and water are weaker than ionic bonds.

C) London dispersion forces overcome the ionic bonds to dissolve the crystal lattice.

Intermolecular Force Practice10) Methane (CH4) is a gas at room temperature. Explain using IMFs.A) Since methane has hydrogen bonds,

the attractions aren’t strong enough to hold the molecules together.

B) Since methane has polar bonds, the dipole-dipole forces are too weak to hold molecules closely together.

C) Since methane is nonpolar, the only interactions between molecules are very weak.