Intermolecular Forces & Properties of Liquids: Key Concepts and Relationships

What are intermolecular forces (IMFs)?

Attractions between molecules that affect physical properties such as boiling point, melting point, viscosity, surface tension, and vapor pressure.

What are the three major types of intermolecular forces?

London Dispersion, Dipole-Dipole, and Hydrogen Bonding.

What is London Dispersion?

A temporary attraction that occurs in all atoms and molecules due to changes in electron distribution, getting stronger as particles get larger or more polarizable.

What is Dipole-Dipole interaction?

An attraction between the positive and negative ends of polar molecules.

What is Hydrogen Bonding?

The strongest type of intermolecular force, occurring in molecules with H bonded to O, N, or F.

Rank the strength of intermolecular forces from weakest to strongest.

London Dispersion < Dipole-Dipole < Hydrogen Bonding.

What is the relationship between the strength of IMFs and viscosity?

Stronger IMFs result in higher viscosity.

What is viscosity?

The resistance to flow of a liquid; high viscosity means it flows slowly, while low viscosity means it flows easily.

What is surface tension?

The tendency of a liquid surface to resist an external force, resulting from cohesive forces between molecules.

What is volatility?

How readily a liquid evaporates; high volatility means it evaporates easily.

What is vapor pressure?

The pressure exerted by vapor when it is in equilibrium with its liquid.

What is the boiling point?

The temperature at which vapor pressure equals the surrounding pressure, allowing vapor bubbles to form throughout the liquid.

What is the difference between cohesion and adhesion?

Cohesion is the attraction between molecules of the same substance, while adhesion is the attraction between molecules of different substances.

What is capillary action?

The movement of a liquid through a narrow space, resulting from both adhesion and cohesion.

Why is water considered special?

Water has high polarity, extensive hydrogen bonding, high boiling point, high heat capacity, and strong surface tension.

Why does ice float?

Ice is less dense than liquid water due to the open structure created by hydrogen bonding.

What happens to molecular attraction when IMFs get stronger?

Molecules attract more strongly, leading to increased viscosity, surface tension, boiling point, and decreased volatility and vapor pressure.

What is the memory trick for remembering the effects of stronger IMFs?

STRONG = STAY; stronger attractions mean molecules stay together, flow slower, evaporate less, and require more heat to separate.

What are hydration shells?

Structures formed when water surrounds dissolved particles, helping substances dissolve due to water's polarity.

What is the significance of water's hydrogen bonding?

It contributes to water's high boiling point, high heat capacity, and strong surface tension.

How do stronger IMFs affect vapor pressure?

Stronger IMFs result in lower vapor pressure.

What is the effect of stronger IMFs on volatility?

Stronger IMFs lead to lower volatility.

What are the key properties of liquids affected by IMFs?

Viscosity, surface tension, boiling point, volatility, and vapor pressure.

What is the relationship between IMFs and energy needed to separate molecules?

Stronger IMFs require more energy to separate molecules.