Chapter 11: Liquids, Solids, and Intermolecular Forces

Intermolecular forces

the attractive forces that exist between all molecules and atoms

Intermolecular attractions

attractive forces between opposite charges; the larger and shorter the charge, the stronger the attractrion

Dispersion forces

the weakest intermolecular forces caused by temporary, random shifts of electrons that create momentary dipoles, allowing nearby molecules or atoms to attract each other; the larger the electron number, the stronger these forces are, the higher the boiling point is; present in all molecules

Polarity and dipoles

Polar molecules have a permanent dipole

Polar covalent bond

produced by differences in electronegativity between bonded atoms within a molecule

Electronegativity

ability of an atom to attract bonding electrons to itself; larger electronegativity, larger polarity

Hydrogen bonding (to N,O, or F), polarity, and more electrons = higher boiling point

Boiling point dependencies

Higher boiling point, viscosity, melting point, surface tension, and lower vapor pressure

Larger intermolecular forces =

Like dissolves like

Solubility depends on the attractive forces of the solute and solvent moleules; nonpolar dissolves in nonpolar solvents and vice versa

Miscible liquids

When two liquids mix in any proportion

Immiscible liquids

The attractive forces between the water molecules are much stronger than the attractions of the water molecules for the pentane molecules; these liquids do not mix in any proportion

Dipole-dipole

Permanent polarity in the molecules due to their structure; molecules must be polar to have this attraction

Hydrogen bonding

An especially strong dipole–dipole attraction results when H is attached to an extremely electronegative atom; a molecule must have O−H, N−H, or F−H bonds. If you have this, you automatically get dipole-dipole attractions.

Ion–dipole attractions

You need ions dissolved in a polar solvent; present in mixtures of ionic compounds and polar molecules

Coulomb’s Law

Describes the attraction and repulsion between charged particles; the strength increases as the size of the charges increases and the length decreases

Surface tension

property of liquids that results from the tendency of liquids to minimize their surface area (increase the interaction of polar molecules with themselves); increased temperature = decreased surface tension

Viscosity

Resistance of a liquid to flow; larger intermolecular attractions = larger viscosity

Capillary action

the ability of a liquid to flow up a thin tube against the influence of gravity

Cohesive forces

hold the liquid molecules together; result in capillary action with adhesive forces

Adhesive forces

attract the outer liquid molecules to the tube’s surface; result in capillary action with cohesive forces