Intermolecular Forces

Intermolecular Forces

​Presenter: Dr. Luis Bello

Intermolecular forces are attractive or repulsive forces that exist between molecules.

These forces arise from the interactions between the electric charges on the atoms or molecules that make up the substances.

Intermolecular forces play a critical role in determining many of the physical and chemical properties of a substance, such as boiling point, melting point, solubility, and viscosity.

London dispersion forces:

1. These are the weakest type of intermolecular force, and they occur in all molecules, whether polar or nonpolar.

2. They arise from the temporary fluctuations in the electron distribution around a molecule, which causes a temporary dipole moment.

3. These temporary dipoles can induce similar dipoles in neighboring molecules, resulting in a weak attractive force between the molecules.

​Dipole-dipole forces:

These forces arise between polar molecules that have a permanent dipole moment.

The partially positive end of one molecule is attracted to the partially negative end of another molecule, resulting in an attractive force between the molecules.

​Hydrogen bonding:

This is a specific type of dipole-dipole force that occurs between a hydrogen atom bonded to an electronegative atom, such as nitrogen, oxygen, or fluorine, and a lone pair of electrons on a neighboring molecule.

Hydrogen bonding is responsible for many of the unique properties of water and other polar molecules.

​Ion-dipole forces: These forces occur between an ion and a polar molecule, such as between sodium chloride (an ionic compound) and water (a polar molecule).

The attractive force between the ion and the dipole in the molecule results in a strong intermolecular force.

The strength of intermolecular forces increases in the order of London dispersion forces < dipole-dipole forces < hydrogen bonding < ion-dipole forces.

These forces are responsible for many of the observable properties of liquids and solids, such as surface tension, viscosity, boiling point, and melting point.

​The strength of intermolecular forces increases in the order of:

London dispersion forces < dipole-dipole forces < hydrogen bonding < ion-dipole forces.

These forces are responsible for many of the observable properties of liquids and solids, such as surface tension, viscosity, boiling point, and melting point.

Multiple Choice

Intermolecular forces are the forces

• within molecules

• between molecules

Multiple Choice

Type of intermolecular force present in I₂, Br₂, and Cl₂.

• dipole dipole

• H-bond

• dispersion

• metallic

Multiple Choice

H₂S has what kind of intermolecular force?

• dipole dipole

• dispersion

• H-bond

• ionic

Multiple Choice

Type of intermolecular force present in HF.

• dipole dipole

• dispersion

• H-bond

• ionic

Multiple Choice

Does CH₄ have hydrogen bonding?

• yes

• no

Multiple Choice

Intermolecular force present in Cl₂?

• dipole dipole

• H-bond

• dispersion

• metallic

Multiple Choice

Does HCl have hydrogen bonding?

• yes

• no

Multiple Choice

Intermolecular force present in HCl?

• dipole dipole

• dispersion

• H-bond

• ionic

Multiple Choice

Intermolecular forces for: NH₃

• Dispersion Force

• Dipole dipole

• Hydrogen bonding

Multiple Choice

Which of the following has the lowest boiling point?

• CaCl₂

• PH₃

• Cl₂

• N₂

Multiple Choice

Which noble gas has the highest boiling point?

• Xe

• Kr

• Ar

• He

Multiple Choice

Which of the following has the highest boiling point?

• H₂

• NH₃

• N₂

• O₂

Multiple Choice

Which of the following will take the longest to evaporate?

• CH₃CH₂OH

• CH₃OH

• CH₃CH₃

Multiple Choice

Which substance would have the weakest intermolecular forces of attraction?

• CH₄

• NaCl

• H₂O

• MgF₂

Multiple Choice

Which of the following factors plays an important role in the identification of specific intermolecular forces in a molecule?

• bond type

• density

• solubility

• molecular polarity