Concept 6 - IMF

What does the prefix "inter-" mean?

"Between" or "among" — like "international" (between nations).

What does the prefix "intra-" mean?

"Within" — like "intramurals" (sports within one school).

Difference between intermolecular and intramolecular forces?

• Intermolecular: Forces between substances.

• Intramolecular: Forces within a substance (chemical bonds).

What determines a molecule's polarity?

The intramolecular forces (bonds) within the molecule.

What determines intermolecular forces between molecules?

The polarity of the molecule.

What determines properties like boiling point and viscosity?

The strength of intermolecular forces (IMF).

What are polar molecules?

Molecules with partial charges at different locations (e.g., H₂O).

What are nonpolar molecules?

Molecules with no partial charges due to equal sharing of electrons (e.g., O₂).

How can polarity be determined?

Using BEND (Bond Electronegativity Difference):

• ΔEN = 0 → Nonpolar

• ΔEN ≠ 0 → Polar (polarity depends on size of ΔEN)

Rank from least to most polar: HCl, CO₂, HF, O₂.

O₂ < CO₂ < HCl < HF

How else can polarity be predicted?

SNAP: Symmetrical = Nonpolar; Asymmetrical = Polar.

What are intermolecular forces (IMF)?

Attractive forces between particles in a substance; weaker than chemical bonds.

Which molecules have the strongest IMF?

Polar molecules

What is a dipole-dipole force?

Short-range attractive force between polar molecules.

What is hydrogen bonding?

Attraction between H bonded to N, O, or F and an unshared e⁻ pair of another molecule.

What are London dispersion forces?

Temporary dipole attractions affecting all molecules; only IMF for noble gases and nonpolar molecules.

What is viscosity and its relation to IMF?

Viscosity = resistance to flow; higher IMF = higher viscosity.

What is the boiling point and its relation to IMF?

Boiling point = energy needed to overcome attractions; stronger IMF = higher boiling point.

Strengths of different IMFs?

• London dispersion: Low (~0.1-5 kJ/mol)

• Dipole-dipole: Medium (~5-20 kJ/mol)

• Hydrogen bond: Medium-high (~5-50 kJ/mol)

Strongest IMF present between:

• H₂O and H₂O

• CO₂ and CO₂

• Ethanol and ethanol
  Back:

• H₂O and H₂O: Hydrogen bonding

• CO₂ and CO₂: London dispersion

• Ethanol and ethanol: Hydrogen bonding